If you haven't done so already, track down Jimmy Boros in MN as he's held the title of key '71-up B-body specialist since Ray Kerkhoven passed away several years ago.

Jimmy is a good guy to deal with and if he doesn't have any louvers may be able to give you some leads.

Ray, before he passed away, had made moulds for both Charger & RR louvers that were quite respectable. If you can find a set of those they would be a great substitute.

Originals have a latch mechanism which is not easy to duplicate, and very few '71-up B-bodies came equipped with louvers (as compared to E-bodies)

Good luck!