I would look at the Social Life page on cavyspirit.com. However, I want to make sure that you know that boars that have not gone through adolescence yet may fight - getting another boar right now may not be a good idea. You may want to consider extending the cage slightly. Make sure that in getting a special needs pig you know what veterinary care it needs, and know the potential cost. Yes, it is very heartwrenching to see all these pets in need of homes, but adopting another one right now may not be the best thing.
If you are still definitely adopting, consider the following factors;
- How much extra money will it take to get another one, especially a special needs one? Do you have money for veterinary care?
- Do you have more than one cage, or the means to get one, for quarantine AND in case they do not get alone? (When you adopt another one it will need to spend 2-3 weeks before introducing)
- Do you know what kind of guinea pig to get? Should you get a dominant or laid back pig, depending on your piggies personalities.
- Do you know how to sex a guinea pig? If no, please check out the page (also on cavyspirit.com) about it. Do not get a spayed female, because the two boars may fight over her.
I would suggest waiting until they are older, but if you know the possible consequences of them not getting along, and are prepared for that, the shelter/rescue guinea pigs will thank you.