For the rubber square O-rings between the gauges and the dash 52, 80, 100 and 120mm for Smith and Jaeger gauges, I know about two alternatives:
1. Use drive belts for tape recorders from Radio Shack. Available in different sizes and cross sections
2. The most practical solution I heard of is to buy Square Buna-N cord stock by the foot at MSC (Manhattan Supply Co) at mscdirect.com or 800-645-7270. Available in square, round or metric ! .098 sq is $0.34/foot, 2mm dia is $0.14/foot, 3/32 dia is $0.10/ft . With superglue it is easy to make whatever you need. These are some sample prices out of their 2004/2005 catalog.
I have not used it yet, but I am sure in MSC ‘s selection the O-rings between the glass and the gauge can be found.
Hope this helps. Robert
I bought some o-rings from a fellow on e-Bay.UK a few months ago..I also got some brand new correct bezels for 2" gauges.. I think he has most everything available as he said that he supplied a few gauge restorers also