It is probably do-able if you have access to a lathe and the skill and knowledge to operate it. Many other aftermarket wheels were not bike specific castings. They had one wheel casting that was used for many different bikes with appropriately machined bearing, brake, and rotor adapters. Examples being Kimtabs, Shelby Dowds, Morris and many others. Are you sure it is a lester and not a Morris? They look very similar and certain year Sportsters came with Morris wheels. Later, Harley copied the design (whether under license or not, I don't know) and cast their own.
Could probably just use a Harley rotor. I have a CycleX offset sprocket that is 5 bolt and was designed to adapt harley wheel to Honda 750...you are welcome to it.
F bike rear lesters were available. Yeah, they are pretty rare. I do have one. I will be using it for the rebuild of my black F3.