There is a bellows available for both the Pentax 67 system and Pentax 645 system, but like all specialist equipment it is expensive:
A better way to go might be to get a cheap 4x5 Monorail (like a Cambo\Calumet) and then replace the ground glass screen with an adapter to mount your camera (basically a 4x5 sheet of 1/8" aluminium with a short extension tube screwed to it). This gives you very long extensions (depending on the camera) as well as all the movements you might want.
Here are a couple of shots of one I made for my 35mm Pentax gear using a Calumet 401CC. It's something any machine shop should be able to knock up in a spare hour (if that).