Sid42
the parts you need are available just not from McIntosh. Lamps and silicone grommets. As you said old were hard and disintegrated.
I installed new bulbs and silicone grommets that hold the bulbs on my old C36
preamp before selling it. Not to hard at all just take pictures step by step. Just
be careful with glass.
McMaster Carr for grommets and Mouser for lamps.