http://www.nrauto.com/sub_index.asp?spage=Gauges
(You'll have to scroll down on the left hand side to see the Porsche Boxster gauges)
There are probably a lot of places to find gauge faces. IMO, they're all priced about four times more than they're worth. I got my techart faces (silver) for $59 off eBay one morning at 2:45 am on night a couple of years ago. NR Auto is $169 per set.
I pulled this site from Excellence magazine, but a lot of others come up in Google searches.
Here's another:
http://meistergaugefaces.com/html/gaugefaces/996.html