There are no spread move TMs available before the first gym, nor do you have access to are tutors or breeding, so we can limit the selection down to just moves the Pokémon available to you can learn by level-up. Technically, you could use the DexNav to get egg moves, but I think that's probably more trouble than it's worth, so I've excluded them. If you want me to include them, let me know.
Treecko And Torchic's lines don't learn any spread moves by level up.
If you chose Mudkip:
- Muddy Water
- Rock Slide
Spread moves learned by other Pokémon:
- Air Cutter (Beautifly, Wingull, Masquerain)
- Snarl (Mightyena)
- Bubble (Lotad, Surskit)
- Disarming Voice (Ralts, Skitty)
- Hyper Voice (Whismur)
- Synchronoise (Whismur)
Sources: List of Pokémon required for first gym, List of TM locations, Treecko/Mudkip spread moves (category 1, category 2), Torchic spread moves, other Pokémon spread moves: 1, 2, 3, 4, 5, 6, 7