If you can't find a mother/daughter pair, try going for sisters or brothers (same sex) pairs, as they will get along. Don't put a male and female together unless you want lots of little babies as guinea pigs are quite easy to breed!
If you can't find a same sex sibling pair and you want boars that haven't been living together, get an older one and introduce a much younger one to him. That way they are much less likely to fight as the older one wil achieve domination over the younger one instinctively.