Hi SalsaandSpice .. welcome to the forum.
Before fostering or owning a guinea pig, it is a good idea to buy some books or borrow some from your local library. I always found it really exciting to read up on how to care for them before you get them, and my daughters did also. The books will advise you about feeding and housing them. Also something to think about before owning is the cost of feeding, housing and also the cost of unexpected vet bills should the need arise for the vets help.
Guinea pigs like to live with companion so getting a rescue bonded pair would be good. As has been said by Poison, give your local RSPCA a call and they can advise you further.
Keep us posted.