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I would contact the rescues in your area and ask them what they have available. Rescues usually have an idea of the personalities of their guinea pigs, and who would be good companions.
Yes, see if you can find a rescue. In general, the rule of thumb is to try an older with a younger, but personalities differ so much. So best to work with a rescue if you can, they will be able to help you find a good match. Good luck!