CB750 discontinued items=tank trim, petcocks, old cams, ripple tanks, good used switchgear, or new, I'll think of some others.
Of course there's that "sandcast" thing and all the parts that go along with that.
A lot of things are available if you want to pay. Good used old style gas cap thumb latches are around, but the finish is usually bad. Take about $40 to rechrome. New ones can be had from Yamiya for $120+/-.
They have repro tank trim too, $100 pair.