OK, I tried the TM-compatible barrel & bucking, and it's a bust.
Similar but different... The worst part is, the TM barrel's OD is larger than Tanfoglio's stock - and stock also has a groove where hop up assembly holds it in place. In short, no easy way of adopting TM to fit a KWC gun.
I did send an email to KWC requesting spare bucking, but would be surprised if I get a reply.
In the meantime, I fabricated a 'J-hop' style thingy out of sculpting plastic, and put the torn bucking over it, followed by teflon tape & dental floss. Basically, made a non hop barrel, albeit not a tightbore. The gun shoots really well, groups are just under 1" from 5m, and there are no 'flyers'. However, I have no idea how long this contraption will survive.
If replacement factory bucking is not to be found, I'll have to learn some mold-making skills to pour my own. I'm so not looking forward to this.