Metropolitan Guinea Pig Rescue recently took in 22 pigs from ONE shelter. If you are considering adopting in the DC metropolitan area, please consider sending them an application!
They do not allow minors to apply for guinea pigs.
They do not allow applicants who have outside animals (excluding farm animals).
They insist on adequately large housing for the guinea pig, such as the housing described at http://www.guineapigcages.com/.
They do not adopt out single guinea pigs.