help please

In D/P pachirisu is your best bet... But aipom and zigzagoon have it, too... There are others but I can't recall them... Anyway, pachirisu is good enough and easy to find in D/P...

You could try to win one as first prize in the Pokemon loto in the TV station, but it's really really hard... All six numbers from any of your pokemons ID numbers have to match the drawn numbers... It's extremely hard since all the Pokemon you caught yourself in your game will have the same number. Any trades or in game trades with NPC's will have different ones. There are 999,999 different combinations of Pokemon loto numbers, so unless you want 100,000 Pokemon with different numbers... It will be difficult...

Oh yeah, I thought I had forgot to tell you something. One Pokemon that has the pick-up ability is the cat Pokemon, Meowth. Phanphy, also has the pick-up ability, so if you have, or can get one of those two Pokemon then you're good.

Yes, there is a way to more Master-balls. You can play Pokemon Emerald, Pokemon Fire Red, Pokemon Leaf Green, Pokemon Sapphire, or Pokemon Ruby, and play the game until you get the masterball. Then, you simply give the Master-ball to a Pokemon so that the Pokemon can hold it, and then you transfer it to Pokemon Diamond through Migration.

You can get get more Master Balls as the top prize in the Lottery at the Jubilife TV station.

Master balls hmmmm other than the lotto and migrating I don't think so

Aipom and Pachirisu have that ability, but you're better off with Pachirisu because he's not so rare.

You can obtain Master Balls if you match all five numbers to your ID at the Lottery Ticket corner in the Jubilife TV Station.

Linoone, zigzagoon, meowth, phanphy, and a lot others. Also, the higher the level your Pokemon is, the more chance it hs to pick up a better item. The best item one can pick is TM 26 Earthquake I think, which requires your Pokemon to be above lv 90.
The master ball can be obtained as the first prize in the Jubilife Lottery Corner. However I find that the best way is to use the Emerald version( If you have it) cloning glitch to clone master balls and migrate them over. It's safe, don't worry. For more about this glitch in emerald, it's hard to explain, but you can go to youtube.com, type in "emerald cloning glitch" and watch the people do it step by step. You should be able to do it it's pretty simple.