There are many ways of gathering any/all of these materials required. From farming Pink Turnips at your own personal Tiller ranch to simply using Herbalism to even killing Tigers in the Jade Forest at the North-East island where the Cloud Serpent dailies are.
Any/all help is appreciated. Every little helps. Yes, potions, feasts and flasks are usually dispensed for -FREE- of charge but how do you think they got there in the guild bank in the first place? Donations and guild-bank money. Please do not rely on the same 1-2 people every month for literally everything; flasks, food and potions - do your part and help out. Help us to help you.
If you need tips on how to collect any of the above materials [simply mouse-over the links to check what is needed for what] then go directly to WoWhead or ask me in-game/via Facebook.