You might want to check with Mr. Nick of Nicks shooting range in Garyville. I see 410 shells out there every so often.
Also check with Shooters Club on Hickory in Harahan, I always see 410 shells on the ground there. Gunny or Devan can get you in touch with Paul the guy that handles the brass and shot shells.
They are a great hull but if you currently load Win hulls you need to get new wads....straight vs tapered hull......I use both and both work excellent with the correct components....the primer pockets tend to be large on the BPI hulls also so you may want to consider a .410 primer pocket conditioner they sell so you get decent life out of them. Quick tap of the hammer and you have tight primers again.