Wide Angle Lens For FF and Contax645/EOS Lens Adapter

After a repeated failed bid on MF digital back, finally I got my
compromised 35mm DSLR.
But then I realized why 35mm FF is not always a good idea, if wide
angle lens is important.

Every medium priced under 50mm has serious cornor light fall-off. Some
have serious color shift too. This includes Canon non-L, Contax-Yashica
35mm, and Rollei 35mm, including prime and some zooms. From what I read
from dpreview's forum (canon/Kodak SLR), the canon L could be better,
but not satisfactory.

The only thing I found acceptible is Hasselblad's 50mm, but again, it
is f4 only. I don't mind to carry the bulky and heavy stuff, because
this is my down graded Med Format. The problem is, I really want a 35mm
lens. Hasselblad only goes to 40mm. The 38mm won't work on 35mm DSLR.

I can find Contax-645 35mm lens. The general comments are it's really
really good. So I really wish there is an adapter for Contax 645-to
EOS. Anyone knows if it exists? I know Contax N would be difficult (or
even impossible) to adapter to EOS, but Contax 645 should be OK.

Or, which 645 format 35mm lens is good too (Mamiya, Pentex, Fujiblad?),
and can be easily adapted to EOS?