Apex used to have a ton of the round meters for the plutonium gauge panel. They're listed as out of stock on the website but I bet if you call they still have some.

http://www.apexelectronic.com/MET13-W-6B

One other thing to note is that to get an accurate face on the round meters you'll have to take them apart and apply a vinyl decal. Pretty much any gauge you can find at this point will have the wrong units on it.