ebay . . . just look search for "autometer lunar gauges" . . i got mine off there about a week ago:
Boost/Vac - $80
Fuel Pressure - $210
I believe one of the companies i got them from was www.thunderboltmotorsports.com . . . on the site they are a little more expensive but just look for the ones they are selling on ebay for a little cheaper
And with eBay you have to be sure you are buying NEW gauages and not something returned by another customer. You'd be surprised at what people are doing on eBay.