I don't think there is any such animal.
First of all I don't think Tanfoglio made the Witness in .45 until after the ban, although I might be wrong.
Also I'm not sure it's possible to cram more than 10 rounds in the magazine. JUST for academic purposes I took a mag a part and looked at the length of the follower and etc and concluded that 10 was about it. However Brownells does sell a extended basepad that will give you 2 more rounds. However I think that actually installing it on a magazine would constitute "manufacturing a high capacity ammunition feeding device."
10 rounds ain't so bad anyway....
regards,
David