[Arran]

Actually, I would consider the 16PX Century of Progress chairside as the rarest of all Philcos.

http://www.philcoradio.com/gallery/1933c.htm#6

Only 75 were made, and none are known to exist. There may still be one or two floating around out there; maybe not.

Along with the 515, I would consider sets such as the Concert Grand, the 52 grandfather clock, and the 1932-33 radio-phonographs (22L, 23X, 24L, 25L, 26J & 27J) among the rarest of all Philcos.

The ones that I am wondering about are a lot newer, like there was apparently a console version of the 40-780 Philco Tropic that I have, and there were a few other Philco Tropic consoles allegedly produced according to the gallery, the table versions come up from time to time but are not exactly common either. I really need to take some photos of my 40-780 (once I dig it out) the catalog picture really doesn't do it justice.
With regard to the counterfeit 515s, hopefully with a little more research a factory marking of some kind will be arise that will stop that sleazeball from pawning off his copies as the real thing to unsuspecting buyers. Then again spreading the word that if party X is selling a 515 that it's authenticity is likely suspect, should be enough, all you would have to mention is that he was contemplating reproducing them, which is true.
Regards
Arran