I was under the impression that Roland arrangers were primarily in the hands (in the US, at least) of the CK Division (Contemporary Keyboards), not the usual MI dealers. CK dealers have territorial exclusivity, which forbids them to advertise on the internet or outside their territories.
So a search on the internet won't bring up a score of Musician's Friend results, and the like. As to Ebay, well, most that have one really liked it, so you might not see too many used ones!
Add to that how few HAVE sold, due to Roland's short-sighted marketing (let's face it, without internet sales and advertising, just how many of ANY brand would get sold?) and obscure dealerships (most CK dealers are primarily piano stores, and their salesmen aren't exactly leaping over each other to get the tiny commission one of these would bring in compared to selling a piano), you actually have to WORK to find one.
I would suggest looking up where the nearest CK dealers are in your area, and calling them... Alternatively, give George Kaye a call. He is one of the few sellers allowed to sell out of his area. Perhaps he can find one for you?
Trust me, if Yamaha and Korg had hidden the PSR and PA series as well as Roland have theirs, nobody would be talking about S900's and PA800's much, either...