I don't know if this will get you anywhere, but you might give Steve Soest a call at Soest Guitar Repair (
www.soestguitar.com) in Orange, CA. The number used to be (714)538-0272. He's got a fairly enormous stock of vintage guitar parts. He may have other pointers as well if he doesn't have 'em.
Another guy with loads of vintage parts is Koz-Ax's Guitars (
www.kozaxs.com). They have a pretty enormous stock of old stuff. They were good for a long time, then the owner left and things went downhill, but I believe he's back now. Again, if they don't have 'em, they can probably point you to someone who will.
Another stab in the dark - try calling Hipshot, the guys that make D-Tuners. They may have a line on some of this old stuff, and if they don't have one, they can probably steer you to somebody who can make the needed mods on a newer Schaller (assuming that the ratio and feel would otherwise match, which may not be the case). The guy to talk to there in the past was somebody named Dave (Borosky or something like that, I think). I've never met anybody that was more of a bass tuning head geek than him. Also, if you can't score a vintage head, you can certainly have them make you a D-Tuner which will match your existing holes so you won't need to change anything around.
Good luck in the search.
David Fung