Out of an infinite amount, they exist, sure.
I mean, lets talk about the Blood War for a while, shall we? The Demons fight with the Devils, but they still only send out a smaller part of their numbers agianst them, while the majority of them aren't there.
But the Demons are infinite.
So that means that an infinite amount of demons are fighting in the blood war since a percentage of infinity is still infinite. To match that, the devils have to be infinite as well, otherwise the demons could just swarm them and kill them with superior numbers. However, there is still attacks made by evil outsiders against the infinite material plane, which the good outsiders sometimes respond to.
That should also, logically be infinite, since no matter how few demons/devils attack the prime, there would still be an infinite of them.
So the Good outsiders have to have the same numbers to compete. Finally, the TN ones have to be infinite to keep track of all the kind of things that could go wrong in the balance among the infinite sized planes, and fix it, so they have to be infinite as well.
That means that at least 2 versions of Good Outsiders have to be infinite, and most likely more since all ethical parts of Good are generally equal in numbers.
To keep check among the Good guys, the NG ones have to be infinite as well, to make sure things don't end badly. So NG, and the other G are infinite. as are LE and CE, and most likely TN.