Master Ball

1. You obtain the Master Ball from Cyrus in the Galactic Headquarters after you've: obtained the first six badges, visited Lake Valor and Verity, obtained the seventh badge, visited Lake Acuity, obtained the Storage Key to access their Warehouse, manuevered through the Warehouse to obtain the Galactic Key to access their Headquarters, and then finally maneuvered through the Headquarters until you battle Cyrus. After the battle, he'll give the Master Ball to you, "insisting" he won't need it in order to catch "Dialga". He doesn't specifically mention the name, but that's who he's talking about.

2. I assume you're talking about Route 210? There are no old Pokemon xP There are just many rare Pokemon to find on that route. Just go on that route and catch all the Pokemon you can, and then go to Celestic Town to follow the storyline.

Well, hello new member. Welcome aboard supercheats, I will see if I can help you out.

You will receive the Masterball from the Team Galactic leader Cyrus, after you defeat him, and his lackeys in the Galactic base in Veilstone City, he will give you the masterball.

2: I do not know what route you are talking about, because you did not list the name of the route in question, remember to give us full details, so we can try our best to help you.

I helped you, have a good one.

For Number 2 I think you need the national pokedex (get it after you see all Pokemon in sinnoh pokedex)then you look for Pokemon and there will be Pokemon from the previous Pokemon games.