If you don't like buying on eBay, finding lenses for the Rollei 35 SLRs will be difficult. Not impossible, but difficult, as the Rollei 35 SLRs never enjoyed a large market share in the U.S., as far as I can tell.
There are three primary lines of lenses: Carl Zeiss designs (first as Carl Zeiss-branded and later as Rollei-branded Zeiss designs), Schneider-Kreuznach and less-costly Rolleinars (reputedly made by Mamiya).
I've noticed lately that Rolleinars are being offered for high prices.
My experience has been great Zeiss lenses -- horrible bodies. I'm currently shooting with a SL 35 E with a f/1.4 50mm Planar and a f/4 18mm Distagon. A really great lens is the f/2.8 85mm Sonnar.
And by the way, does anyone with a Canon camera shoot with a Canon lens?