Original Radio King parts do come up on ebay from time to time, but its a waiting game sometimes. If you can live with non-original chrome plated lugs, they do make reproduction beavertails now. The later sound-king lugs are being reproduced as well, as are stick-saver hoops. Also, there is a source for stick-chopper hoops too, but they are more Gretsch-like than Radio king-like and they are not engraved like radio king hoops are.
Sorry, I'm not of much help, but this is my first Slingerland resto as well....but so far that's what I've found out there....