I have some thread-on adapters removed from e-bikekit 180mm discs, but to use them you'd need to secure them to your own discs. Originally they were riveted to the discs they came with; you could probably use nut-and-bolt, though.
The holes are not ISO standard, but whatever is probably typically used on Chinese discs. So you would also need to either file the holes in an ISO disc outward to match these, or get discs with that pattern already.
Anyway, I can send you one for the cost of mailing it, if you think you can DIY enough to make it work--it should fit in a padded envelope and thus probably cheap to ship to you in Utah.
Choppers US sells one,
http://www.choppersus.com/store/product/308/Disc-Brake-Rotor-Converter/
and I thought that E-bikekit.com did, too, but I don't see it anymore.