Two sources come to mind, neither of which are very practical. Dan at D'Antiques had - past tense - an excellent data base of some 4000+ tapes online, with sonic ratings, images of boxes, and detailed reviews of tapes, when such were submitted by readers. That database has been removed and no longer available. It's a testament to the fact that online data is ephemeral and could disappear at any moment. The second source is the review of tapes printed in High Fidelity, Tape Recording, and Saturday Review magazines of the era, i.e. 1955-1960. These are available in some libraries. Of course it would be wonderful if someone compiled these and published them online.