Campy Rear Derailleur Spares

[GScot]

Picture to make things clear. The B Screw Stop / Sleeve with a tab that engages the stop on the hanger. I need one for an Ekar rear derailleur.

Had a bike shipped in and it arrived with the rear wheel in place and the chain & derailleur assembled. No apparent abuse of the box or other damage. The front wheel had been somewhat loose and had intertwined the rear derailleur. I'm reaching for the explanation but that's all I can point to for cause. The tab labeled B on the attached pic is broken off. I even found it in the box after going back on a search.

First noticed that the shifting was out of spec, rubbed to the outside on the small cogs, toward the inside on the big cogs. Pulled the derailleur and grabbed my alignment tool. Hanger was bent. Straightened and found the new problem when I tried to reinstall the derailleur.

I'd love to find out what the part number is and buy a replacement if this is available. I really don't want to buy a whole new RD. I'll be happy to buy a wrecked derailleur if anyone has spare parts. And if anyone is aware whether this part can be scavenged from a 12 or 11 speed derailleur.