Welcome to SBO.
One place to start might be the parts manual. It can be found in the Catalina 27 owners' resource section of the site.
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You might also search the SBO Store here. A lot of Catalina parts are available.
If that is unsuccessful... Try Catalina Direct. Bit expensive, I am told, but again, parts are often available.
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And a last resort is to take your current part and use it as a template. White Oak or even Ipe are potential long-lasting woods for boats in fresh water. That is, if your DIY wood skills are fair. It would be a good project to test your woodworking talents. Boat Owners save boat bucks by applying DIY skills to many of the things that will require fixing.