Medium format lenses don't normally have large apertures... Something to do with depth of field becoming impossibly thin. That being said, if you have heaps of money try the Zeiss/Hasselblad 110mm f2 and let me know how it looks.

In terms of lenses that can be adapted there are a lot of them. Try Pentacon Six lenses, Carl Zeiss makes a ton of lenses in that mount. Hasselblad lenses are another option.