The short answer, I’m afraid, is that you’re a little bit screwed here.
The issues of AVENGERS and NEW AVENGERS that are part of INFINITY are braided into the main story so completely that you cannot collect it without them–the story won’t make any sense whatsoever. So that’s what we did with the collection.
I didn’t want to do single collections of just the AVENGERS or NEW AVENGERS issues for the same reason–those collections don’t make any sense as stories on their own. But it was argued that there are readers who like to have all of their books in a run in the same format and numbered sequentially, and if we skipped the next AVENGERS volume to being issues #24-28 or whatever, readers and retailers would be upset.
So now, there are readers and retailers upset about the way we ended up collecting these stories.
The easiest way to fill in, I would think, would be to go digital. But even if hard copies is what you’re looking for, there were enough of them out in the marketplace where they shouldn’t be too tough to locate.
Sorry about that. Good luck!