How to find low bitrate audio (non alac/flac)
In iTunes, go to the menu View -> View Options.

Expand the File triangle, and check “Kind”

You can now sort your songs by file type by clicking on that column header, and they cluster by album.

Alternately, make a smart playlist that includes files by their kind or size, and use the View dropdown in the top right to view it by Artist List (or Grid, but I assume you have your music collection sorted by artist.)