First of I have like a couple questions 1.) where do I find Regirock..

1.) Regirock, Regice and Registeel... Wow, what a huge ask! First you will need a wailord. (catch one on Route 129, by surfing, maybe fishing. They're rare.) or evolve a Wailmer at lv40 into Wailord (Wailmer can be found pretty much anywhere there is sea water by surfing or fishing) Then you will need a Relicanth. Catch one of those Underwater (dive) on routes 124 and 126. They're rare, too, but you need them to get the three regis. when you have these two, you need to go to Pacifidlog town. You need to have the two Pokemon aforementioned in your party, it doesn't matter where yet, but it will later, so just keep them with you. Also have a Pokemon that knows dive, and one that knows dig. Surf west (left) of Pacifidlog, and here's where it gets tricky. You know how the currents pull you along, just before you get caught up in the currents, stop! Surf down to almost the bottom of the currents and you'll see one row of currents going across the screen that starts further left tan all the others. Surf into the currents here... There is a specific way to go, but just try not to end up surfing too high up every time you stop. You will hopefully keep going west (left) and get to a small dark square of ocean surrounded by currents. (I can provide you with an exact step by step walkthrough for this if you want, just ask for it from me in the questions section)

Divw down into the currents. Then you will come to some braille in the wall here. Read it and decipher it. (your game should have come with a braille decoder... If it didnt, you will need to go online and find the braille alphabet, because it's the key to getting the regis) anyway it tells you to "go up here" only use dive right where the sign is. If you use it anywhere else underwater there, youll just go back up to the surface, but if you use it there, you will find yourself in a cave. In the first part of the cave, you will find heaps more braille. Reading from left to right, top to bottom, it is the alphabet, and comma and period (full stop). So you could use this to help you decipher.

In the wall in front of you there is some braille that says "dig" or "use dig here" or something... If you do in front of the braille, a door will open in the cavern. Go in, and you will be faced with an empty room with more braille. This has some story, I think, and something along the lines of "first comes relicanth, last comes wailord" (or it might be the other way around) well you have to put the two Pokemon in your party as it says. Relicanth
Any pokemon
Any pokemon
Any pokemon
Any pokemon
Wailord

(or the other way if that's what it says to do)

And look at the writing again, and a rumble will happen, and you will hear a farr off rumble or clicks (it will tell you with text that you've heard something, anyway.) This means you will have unlocked the regis!

You may have seen ruin maniacs around... One in the desert, and nearby a huge rock with six smaller rocks around them... These now have doors in them. Beyond those doors are a room with braille instructions on what you have to do (which involves going to the center of the room and using fly, or walking left and using strength, or waiting for thirty seconds or something like that... Theyre pretty cryptic-sounding, but simple enough to get. to get regirock, you must find the desert ruins in the very southern part of the desert.
To get registeel you need to find the ancient tomb on route 120 (near the little girl who gives you a rare berry, there are steps up).
To get regice you need to find the island cave which involves surfing up route 105 and searching about there.
They are all at lv40.

2.) Latias is randomly encoutered in sapphire after you have defeated the elite four. You will hear about it at home just after you restart the game after defeating them. I would suggest you save your masterball for this one, as it runs away whan you encouner it, which is random, so it is hard to get!

3.) You need to trade Machoke to get Machamp. It evolves via trade.

4.)shelgon evolves from Bagon. You may fond these in a small part of meteor falls, deep in. It will evolve at lv30 into Shellgon then at lv50 into salamence.

If you have beaten the elite four, then you should have already known about Latias... Just look everywhere, like a regular Pokemon encounter, in grass, or in water. (not in caves) I caught a metagross in Colosseum at lv60... Your point? What other Pokemon do you have? :-D

1.You may find the Regis after you've done with digging.
Here are the steps to do that:
Get a RELICANTH{in any lvl}and a WHAILORD{any lvl also}.
RELICANTH is found in any place when you DIVE.
WHAILORD can be evolved from WAILMER at lvl 40 or be gotten in routes 124 and 126 but it is rare so I suggest you evolve WAILMER.

Put them in this order:{Here is an example of the order but RELICANTH and WHAILORD are in their place}:
RELICANTH
KYOGRE{any pokemon}
BEAUTIFLY{any pokemon}
DUSTOX{any pokemon}
SLAKING{Any pokemon}
WHAILORD

You have to get the ability Dig from an ordinary Pokemon or from TM27.

REGIROCK:Is in the desert where sand dwellers are and a POKEMANIAC which fight you with a SANDSLASH only.Keep going down till you find a cave which opened after you digged the lair.

REGICE:Where you SURF to Dewford Town when Mr.Briney gets you there first he goes to the left and keeps going down isn't that right?Then he goes to the right from this place there is an island where a pokemaniac is there go on it and then SURF again to the left then you will find a swimmer.Leave him and go up you will find a cave which was opened after you have digged the lairs there you will find REGICE.

REGISTEEL:In route 120 where you fight Ruin Manic Chip you will find a large rock surrounded by six rocks which will be turned into a cave after you digged the lair.

2.LATIAS os to be found in any place where GRASS is or with any place where water is only by SURFING but cannot be found in any caves.

3.MACHOKE can only evolve to MACHAMP bi trading it to a friend only because it can't be digivolved when it is caught.

4.SHELGON can be evolved from BAGON and it is found in METEOR FALLS deeper in.

HOPE I HELPED.