They're called Air Vents. LMC lists new seals [p/n 38-7420] and knobs [p/n 30-2630]. My catalog is old so you'll have to look up current pricing.
Clean them up. If you're lucky the little 1/4'' dia. spring-loaded pivot pins at 12 0'clock and 6 0'clock aren't rusted out. They snap into 1/4'' holes at 12 and 6 on the cab kick panel.
If they're AFU, you'll have to source them from junkyards, parts dismantlers, WTB ad, the usual. I call them ,,Mexican A/C''.
EDIT: Good news -- LMC now sells repro vent doors. P/N: 38-5348 [+9] Bad news -- they're $50 each.
Hey Kurt, You were looking for a better solution to pot metal heater control levers?
Here you go:
www.oldairproducts.com
P/n: 50-7725B ''67-72 Chevy/GMC Non-Air Heater Only, Lever Controls w/ Black Face'' [Steel]. ....$28.50
GMail sent.