Supernova Tactical mag extension clamp

[BookCop]

I have a Supernova PG Tactical on order. I bought the TacStar magazine extension. What tube-to-barrel clamp will fit? Better yet, what clamp will fit and add a sling mounting point? None available that I have found specifically list the Supernova, but Choate, TacStar Mesa Tactical and DMW make them for the usual suspect shotguns. Something must fit...

Thanks in advance, B