Thanks for the ideas and encouragement guys. I was at my mom's house tonight and we were talking about it and she thought of one last place to check. She found the loan documents and they had the VIN! I had already been in contact with Barry Washington, so I emailed him immediately.
His reply follows:
The good news is that yes, I have heard of it.
The bad news is that it is in Japan. There is actually a photo of it on the website at http://www.challengertaregistry.com/photos/members_cars/sn310331.jpg
I have not heard from the owner in quite a while, hopefully he & the car survived the earthquake & tsunami.
The stripes & graphics on it were painted on before he bought it, but it is coded for black stripes. There is nothing unusual about its order number or tag data, so it definitely was not a 'special order' from the factory.
I can try sending him an email if you like? I am sure he would like to see your vintage photos of it.
So there it is, all the way in Japan....