Thanks for the suggestion. I called Zenith (now LG Electronics) twice.
First to talk to "customer service" who never heard of Heathkit and
said they don't carry manuals. She had some trouble formulating a
complete English sentence, so I didn't trust her reply.
My second call was to "parts". After 15 minutes on hold, I decided it
wasn't worth any more time, given the (un) likelihood of a positive
response.
Well, I guess I'll try one more rec.radio.amateur subgroup and see what
happens. Hope springs eternal :-)