My search was hopeless. I tried everyplace I could find that may have one on the shelf. I eventually talked to a very helpful guy with an acceptable solution. I'm pretty sure he was a tech at Woody's Cycle & Marine in Michigan. He claims to have done several boats this way, and it sounds much better than filling the void with silicone. So I followed his advice and used a Chimney Boot that is readily available at hardware stores. I happened to have one on a shelf that I had bought years ago and not used. It is made with "steps" so that it can be cut to fit various size chimneys, so sizing it was fairly easy. I did the work yesterday and am very happy with the results.
The one I had on hand was Oatey Universal Pipe Flashing. Part #14052. But there might be a better one out there. I had this on hand, and it had the right "steps" for this application. The hardest part was how to drill the holes in rubber. I used an old bullet casing I also had on hand. I had used this trick before to punch holes in rubber. Using the casing gives a nice clean hole.
All said and done, it was a good solution. Looks good and if it lasts longer than 2 years it will be better than the OEM that I replaced, and is apparently obsolete. Although if someone happens to find a source for the OEM or a replacement, I'd still like to buy the correct part.
Hopefully this will help someone out that needs the same part.
Cheers,
Ron