Have you tried calling the shelters not just looking at there online pages. I know my local shelters hardly ever lists them, if at all. I am currently looking to adopt and had to call around to find a shelter with guinea pigs. So try that then get back to us.
The reason not to get a guinea from a petstore is stated in almost every thread in the kitchen. We don't support it, period. It gives money to the people we are trying to stop. Also when buying from a petstore 95% of the time you are going to get a sick animal. So why go through the trouble? It will do you better in the long run to try and adopt.
And like PiggieMom said there are always piggie trains. So don't think buying one is the only way. If you truly want a pig bad enough you'll find a way to make it work!
