I had gotten pricing from Brian at Tiara for switches on our 2008 3900 Sovran. I'd lob a call into them. If they can't get them for you, they should at least be able to tell you the part# etc.
The 1990 33 uses old style switches. You should be able to find these at your local boating supply store (West Marine, Boaters World, ect...). If not, they should be able to order them for you. Tiara is only going to have the newer style switches.