(2) Go to Mossdeep City & into Steven Stone's house (upper-left house)
(3) Have 5 Pokemon in your party and pick up the Pokéball on the desk
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it should be 20 like in ruby/sapphire
Beldum cannot be caught or given as an in-game gift in FireRed. You'll have to trade one from Ruby, Sapphire, or Emerald in order to get one in the game.
As of Generation Four, and Probably Generation 5, there is only one Beldum. In Ruby, Sapphire, or Emerald, after beating the champion, go to Steven Stone's house on Mossdeep City, and he has left a pokeball and a note, saying that he has given you Beldum to keep. So, you CAN catch Beldum in an Ultra Ball, but there are no wild Beldum TO catch in an Ultra Ball.
You could get one, but you'll need to trade it over from Pokemon Sapphire, Ruby, or Emerald.
You can find Devon in Mossdeep City he will give a Beldum. Note: Also works for Ruby and Sapphire.