I'm a fan of 11-48s, and have owned them in 28, 20 and 12 ga. Still own/shoot the 12..and am trying to refinish a butt stock replacement I was finally able to track down. Guess what I'm trying to say is this~they can be a royal pain to find parts for, and anything BUT 12ga. is even harder, and more $. For barrels, you'll probably have to bring-up from the US...and I'd contact Clay @ Prophet River for fees/time lines to do that. I bought a hard-to-find Remington barrel on eBay a few years ago, and had Clay bring it in. Searching for your .410 barrel, I found at least a couple of hits on ones that did sell on eBay. SO...while I'm no eBay fan, I'd urge you to get some $ in PayPal money, keep an eye on eBay, and familiarize yourself with PRs rates, and who you have to get the barrel shipped to. (a gun shop in Montana)
At the same time, post WTB ads in an many places as possible...and cross your fingers. I've messaged a couple of people I know on the off-chance they have a lead for you. Same guys I've messaged about other 11-48 stuff..so they won't be surprised. lol
If anyone needs a 12ga barrel, receiver...lmk.