Our local Animal Control facility does not deal with small animals and our local Humane Society claims that they don't kill any small animals. For some reason after all their years in the valley, people don't surrender very many small animals to them. I think they are full of bull and don't believe it. (They have been known to lie about their stats in the past as well), but at this point, we don't have a relationship with them to pull guinea pigs, because they claim they won't run out of time.
Every community is different and you will probably have to meet with the executive directors of your local facilities to find out what their policies are and what you would need to do to qualify as an outlet for guinea pigs. Once you have established yourself as a responsible rescue, they will generally waive the fees for you in order to keep the animals alive.
If you just go in and tell some volunteer that you are there to save the guinea pigs, they will probably laugh at you, yet let you adopt them all for the regular adoption fee. :-)