no
Trade.
First, you have to complete the Battle Frontier COMPLETELY(Gold and Silver)!! Then, Proffesor Birch will call you and talk to you in his lab. Then, he will give you another starter of your choise(Torchic, Mudkip, or Treeko).
if u picked torchic as your starter the trendy phrase is "Top Torchic" and search the tile at the bottom of the lake. if u picked treecko as your starter the trendy phrase is " Happy treecko"and search the tile by the waterfall. if u picked mudkip as your starter the trendy phrase is "Just Mudkip" and search the tile way bottom of the lake. Note: this is only Pokemon ruby,sapphire,and emerald after finishing the elite four and must obtain super rod.
In Ruby, Sapphire, and Emerald, there is only one possible way for another trainer to have a Mudkip. In the beginning of the game, you have the option to choose one starter Pokemon. If you choose Torchic, your rival will choose Mudkip. Your rival will always take the Pokemon that is elementally superior to yours. You choose Treecko - They choose Torchic You choose Mudkip - They choose Treecko You choose Torchic - They choose Mudkip
The starters are: torchic (fire) treecko (grass) mudkip (water) by the way, Torchic becomes part-fighting type when it evolves, and mudkip becomes water-ground type when it evolves.
Trade.
Answer to get both simply trade :)To get mudkip or torchic you can start with mudkip or torchic at the beginning of the game but you do need to trade to get the ones you don't have.
I think Wingull is the better Pokemon if you got Torchic or Treecko as your starter because it evolves into Pelliper at Lv. 25 and he is Water/Flying, giving you a much needed water. If you picked Mudkip as your starter though you could go either way. But overall Wingull/Pelipper is the better option in the long run.
You probably caught it at pal park. This means that you migrated it from ruby/sapphire/emerald version. There is no way to catch a mudkip without cheats in Pokemon diamond. I'm sorry to say that it is impossible to catch in Diamond without migration or cheats: This is the guy who found torchic (not in pal park). I found it licking honey off a tree.
The only way to get the other two is through trading. You need two GBAs and a link cable.
the only way i can think of is to trade with someone who has a mudkip.
I think you meant torchic, the only way to do it is when prof. birch is in trouble choose torchic to save him. you can't meet torchic in the wild but.