The standard Sinar bellows is about 14", so you might be able to use a longer lens of tele design (probably the Nikkor 500mm T-ED will just get to infinity, and could be more usable with an extension lensboard). If you need more bellows, then you add a rail extension, extra standard, and another bellows. Used Sinar stuff is plentiful and not too expensive. If you get a bag bellows anyway for wide lenses, you can use that in combination with the standard bellows, figure $50 for a 6" extension rail, maybe $150-200 for an extra standard (or even cheaper--just buy a second F and sell off the parts you don't need). You might even find an F or F1 to begin with with standard and bag bellows, which is a fairly common setup, and you would only need to add the extra standard and maybe more rail.
A Technika has 17.5" of bellows, so a 500mm should work without modification.
I think the Canham DLC has 20".