Looking For New Old Stock Source

I'm looking for a good source for new old stock (GM). I need parts for the cruise control (specifically the control unt/amplifier unit) on a
1990 Suburban. The only parts I've been able to locate locally are Cardco reman. and the last one of those I bought lasted only a short time. Mine works as long as you keep it cool (by keeping the cab cool) but soon after you turn the heat on, it cuts out. I really don't like freezing just so my cruise will keep working. BTW is there some way to do a bench check on these things?
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% "So why do I drive a big SUV? It's because I have to haul numerous people and things to places." ~ R. Lee Baxton ~
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