IDK about a "supplier" anymore outside of watching ebay and the LF-related(APUG, LFF, AZO forum) regularly. Up until 1yr ago or so, it seemed there were (1-2) 47.5" RDA's that hit the interwebs for sale, usually by people selling a former graphics art company's "scrap metal"....
I got mine(which is now with a nice chap in China) from a friend. Was intending to make a specialized long-FL tele 8x10 camera, but that project didn't fly... So I sold the lens onwards.
put up a "WTB" (want to buy) listing and see if anyone pops up with one for sale. Might take some doing though, and some patience, especially if you intend on getting one "inexpensively"...
best of luck!