Hi Bob
Yes I have looked into buying copper sheet and the composite material and then making up the gasket myself. Maybe I could get the sheets CNC cut , I would need to provide a computer file in the commonly used CNC format, something like G code ?
Yes the stationary engine guys and clubs would be a good place to ask.
There are a few people who can hand make vintage car gaskets for the car restorers but these guys are very expensive $$$$. There is a on-line business in Thailand that manufactures head gaskets for vintage car owners, I got a quote some years back... upwards of $300 plus $100 shipping for just one 6 Cyl. head gasket.
https://gasketstogo.com/
Auto surplus, a business here have NOS Morris head 6 cyl. gaskets for the 1933 to 36 models, but Morris changed the gasket shape in 1937 and I need the 1937 onwards gasket.
Back to the broken bolts, I have drilled out one of the broken M6 bolts and it worked out OK. I have not used heli-coils before, so this has been a learning experience ! In order to achieve a nice and accurate hole, I bought a cheap mag drill. The drill has a electro magnetic in the base , so that you can, with a switch, turn on-off the magnet, the drill has to sit on a flat even steel/iron base, it can be used horizontally too. I made a little aligning tool out of angle plate, the holes in the plate are the correct distance from the block deck. The clear plastic rod has cross hairs like a rifle sight . How it works: you look down the rod and line up the cross-hairs in the centre of the broken bolt. You then align the drill in the mag drill in the angle plate hole and drill out the broken bolt. The Heli-coil set comes with a special sized drill and tap and the little stainless steel coils. BTW there are many cheap copies of heli-coil sets around, the Chinese sets are of dubious quality , I found a brand that is actually manufactured here in Aust.