I don't think a lot of people have Fintails, at least not here in America. In the past ten years, I've only seen one Fintail on the road besides my own (although I heard reports of another local Heckflosse sighting a couple years ago). I think so many of them have rusted away over the years that there are very few left in operational condition.

That being said, there probably isn't any big on-line presence for Fintails besides the resources listed above. But they are still excellent vehicles!

Now to your question about wheels: I would recommend that you not bother with 14" wheels. You can get 185 80R13 passenger car tires (the correct size) from MAXXIS at an OK price:

4 New 185 80 13 Maxxis MA-1 Tires P185/80R13 90S 1858013 | eBay

I use those tires on my vehicle with good results. I had them mounted by a local mechanic at about $15 a tire.