You could try Dave Evans. He races in the USCRA in northeast US. He is a very nice guy and was selling his cb550 race bike(has was a multiple USCRA champ in middleweight on cb550s). He may have something for you or know where to look/ask.
Dave Evan's email: oldbikeracing@juno.com
Here on the forums, Brent Waller (BWaller) and Scott Mckenzie (HRCScott) road race cb550s, definitely people I would ask.
I'm into 750, so I'm not much direct help to you. Good luck
George