Where can i get lots of guam leaf and is waterbirth the only place to collect snapegrasss?

Snapegrass also spawns on the Hobgoblin peninsula southwest of Falador, near the crafting guild.

For guam leafs i would just go to chaos druids, people usually drop them and there a common drop so just get an inventory tele to fall and go back, or edge dungeon just as long as you dont get skulltricked.

If you are willing to pay, the Grand Exchange may have guam leaf for sale... otherwise, use the Chaos Druids. As for snape grass, it spawn on Waterbirth Island, and the Hobgoblin Peninsula. There are also a few monsters that drop it, although that is seldom.