If you cant get the orig parts, get a generic one-
Since the old chevy IDI's are a dime a dozen and you can get them abandoned all over, you could probably get one from them - just sitting right under the intake.
You could alos just order one for them (or another truck that has one) and use it. Not sure how cold you get but they should work okay. You could hook up a switch as the ones they have usually are alway off untill 20 deg F or something. Hook up a cockpit toggleswitch or something.
Napa here in town has a whole assortment of filters, tanks, etc. , sure they have a heater.
Also, do not know if it would work, but maybe you could use the atf deal and hook use it for fuel instead of atf, if it is that cold you would not need the atf deal anyway, or could just use a diff. cooler. Just a thought.