You can try getting it from different people but dont think that will really matter 2 much since the ones ppl sell are from the same parent. By the time babies grow up and are mature enough to breed as well, the previous parent can lay almost 100+ more babies.
As far as how many you can have in a 30g.. it all depends on how many hiding places you have and ofcourse whos with them. They like to hide and are safer that way, the more they bump into each other the more they fight (even though they are peaceful they still have to defend themselves) But i would go with 6-8, see how they do, if any breed, and then work from there.
