These may be worth a try. I know I love my Super Max .675 for my Rem 870. And I have heard the Star Dot choke does well in the Invector Plus guns.
http://www.ebay.com/itm/MAD-Super-Max-Hevi-Shot-Turkey-Choke-12ga-Invector-Plus-Perfect-Condition-/181125817330?pt=LH_DefaultDomain_0&hash=item2a2bf0a3f2#ht_89wt_919
http://www.ebay.com/itm/Star-Dot-12Ga-Turkey-Choke-Tube-Invector-Plus-Perfect-Condition-Rare-Find-/181125811607?pt=LH_DefaultDomain_0&hash=item2a2bf08d97#ht_89wt_919