If you have done a "backup" (that's where you email yourself the contents of your library and playlists) you can restore from that.
If you haven't done a "backup" yet, do it now (through the "hub" icon).

There are several versions of Avalon posted in the forums. You can find them by pasting this search-string in a google search field:

"avalon" site:irealb.com/forums

You can also try using the search feature in the forums....
If you find that Avalon is only available as part of a playlist, don't worry. Just download the playlist. The app will only actually download only the tunes that are different from what you already have in your index.
)BOB