I had to replace mine ('79 K) several years ago. They're readily available, locally, either at Wal-Mart or an auto supply store. Be sure to replace all of them! You really do not want to repeat the procedure any time soon, as it is a hassle. The gauges have some type of dampening fluid in them, and the Clymer manual cautions against leaving them face down too long, as the dampening fluid may leak out. Don't panic about it, just don't leave them face down overnight, or any longer than is necessary. I never had an issue, just an FYI. Cheers!
1979 CB750K (sold, 2012, but not forgotten)
1983 Kawasaki 440 LTD Belt Drive (sold, 2011)
1993 Kawasaki Voyager XII