I would just get a PayPal account and make a post or two on the Facebook pages for retrobike people. Klein, Schwinn, Cannondale, and Vintage mtb all have their own pages. That way you don’t have to deal with eBay.
New to the forum, but just got a Schwinn Homegrown that I’d love to convert to a flat mount disc. I would actually buy a few of them depending on the price.
If you want to reach out to the Schwinn Homegrown Facebook group, myself and several others will likely buy some from you.
Best,
Drew