A possibility for the Wish List: "K-On! Anthology Comic Manga", a hybrid.
These are K-On! strips by other mangaka.
The only place that I have seen it is on a scanlation site.
I think that it is just in the magazine and not in a book yet. The translation says that it is published by Houbunsha, the company that published K-On! and Hidamari Sketch.
The original title is けいおん! アンソロジーコミック, I think. Perhaps somebody who reads Japanese can check the Houbunsha web site
to see if there is anything about a book.
It would be very nice if there is a book, either now or in the near future, and it is licensed by Yen.