What is the project, or is it safe for you to divulge?
What focal length range are you interested in? How much area must it cover? Does it need a leaf shutter?
Mamiya TLR lenses can be quite cheap, and come in pairs, one with shutter and iris and one without. Removing the lens assemblies from their mount plates looks pretty straightforward, just a lock ring and the wire connecting the flash connection. These cover 6x6 and no focusing mechanism.
Bronica etr series lenses seem pretty cheap too, cover 6x4.5, and have no shutter but do have an iris and focus helix. Similar lenses are available for Bronica's 6x6 and 6x7 lines.