Hello Karen & welcome to MobileRead. I don't know how many books in the download forums are in .RB format, but with Nick's
Mobi2imp program you can convert any of the MobiPocket books here into a format that can be read on your RCA device.
Glad you found us here @ MobileRead. Just for nostalgia, I've been thinking about buying an eBookwise reader, which appears to be just a newer generation of your RCA one. (I'm not sure hubby would understand why I think I need yet-another eBook reader, though.)