You didn't mention your location Jim; but a good place to
start might be your local McIntosh dealer. They often work
on older Mac equipment from the late 60s on - and if they
can't repair your gear, they will often know who can.
I just recently had my MR-73 Mac tuner (a late 1970s
unit) completely refurbished; and my local Mac service dept.
was able to get a replacement part that is no longer made
or carried by McIntosh quite easily. The tuner now works and
looks like new - and the reception is wonderful.