In Resident Evil: Revelations for the Nintendo 3DS, you can unlock infinite ammo for the rocket launcher, however it won’t be easy.
To unlock infinite ammo for the rocket launcher, you’ll need to beat the game on Hell difficulty, which is the hardest difficulty in the game. You unlock Hell difficulty by beating the game on at least Normal difficulty.
Check out my other article for the full list of unlockables in Resident Evil: Revelations for the 3DS.