If you are referring to the deck fills you can buy replacement blue caps at Catalina Direct.

These?

[url]http://www.catalinadirect.com/index.cfm?fuseaction=product.display&produ...

Just as an fyi. I had those caps on my 1988 C30. One spring my diesel quit; water in the fuel. 2 gallons of water in the fuel. I couldn't figure out where it came from, but eventually traced it to the cap. Evidently the recess for the winch handle had filled with water, frozen, expanded and cracked the bottom of the recess all the way around. Melting snow and rain must have run down the deck, into the recess and into the tank. Strangely enough, another Catalina in my marina had the same problem that winter.

Maybe an isolated incident, but I put tape over the caps each winter after that until I traded the boat on my C36.