Good question.....I had delt with this myself.
I had a collection of NOS and used Sun instruments/tach for a modern drivetrain project, like a LS1 or LS2.
I found this company online who had what I needed, but sold all of the SUN parts on ebay ($$$$ !!) after I decided to use modern gauges. Try these guys, I think its who I talked with. Might be more online too.
http://www.instrumentsrus.com/sun.htm
bty...there is a lot of info online about this, seems like many have the same application.
Good luck,
Jeff