Thanks. I found another RCA compilation, Bunny, which appears to have been released only on LP and MP3. There appears to be minimal overlap between Gangbusters, Bunny and The Pied Piper. It is a bit surprising that these appear to be the only legit reissues.
Going by memory, most (if not all) of those tracks are on the Mosaic. That might be the way to go for someone on the fence about investing in the Mosaic, which is an absolute treasure trove.