If congress passed a law today that made it illegal for a convicted felon to own or possess body armor regardless of how they came to own or possess it, the supreme court likely would:

I believe the answer is: find it constitutional under the Commerce Clause.

The commerce clause stated that the congress has the full power in regulating our country's relationship with another country regarding trade activities.
So, it should be fairly easy for congress to make law that determine the legality of various products