There are several Web sites that allow users to place ads for pets available for adoption or sale, such as Simple Pet Care and Pet Classifieds. Both have baby guinea pigs available.
Keep some basic guidelines in mind when adopting a guinea pig. Guinea pigs are very social so it is best to keep more than one. However, they should be of the same sex unless you have plans to breed them. Guinea pigs generally live for five to seven years, so a potential owner must be prepared to care for them for a longer period of time than most other small pets.