Carl, do you own a Sporting Clays Classic Repro? If so, please chime in the SCC Repro chamber thread...
Parker Repro SCC guns were originally fitted with Winchester Winchoke "Invisible" choke tubes. I purchased a couple of these NOS choke tubes from Chris Showler of Double Eagle Trading Co. in Grass Valley, CA Chris can be reached through the attached link:
http://doublegunshop.com/showler.htm
I believe Brownell's also has them:
www.brownells.com
Browning and Mossberg among others, also furnished tubes that are also compatible.