I've never seen custom sized mounts offered for sale from any vendor. There are a lot of custom mounts, all home made. Creative Engineering is working on a kit for the 2 stroke into a Schwinn Jaguare frame which requires a special front mount. I'll look and see if I can find a couple of links to threads that have been posted regarding mounts.
And, I want to see a good pic of your coupe. Is that a generator I see up top?