I wonder if simple close-up lenses will work and give good optical quality? I don't know the specific optical formula of the Rolleinar close-up lens, but it can't be too too special because they weren't tuned for Planars and Xenotars as separate lenses.
So an off-the-shelf close-up lens with a Bay III to XX thread adapter. Move it from top to bottom lens, raise camera, for actual exposure. Along with the rarity/collector value, you are paying for a nice prism to shift the viewing lens image. Eliminate that and things get simpler.
Also, put out a Want to Buy here and on other forums like rangfinderforum. People are more reasonable all in all. And put up an ongoing search on Ebay in the hopes that someone throws up a set at a reasonable price. Patience!