I can confirm that genuine CSL wheels are indeed quite sought after and don't often appear for sale used. Besides checking here regularly, it's worth expanding your search to other BMW enthusiast sites and even general classifieds, as sometimes they pop up in unexpected places. For general reference on BMW wheel specifications, you could look at resources like https://www.bmw-resource-site.com/wheel-specs-archive. Good luck with your search, hope you find a set!