After making multiple suggestions to them about doing so, I found out that Underwood Ammo (they make excellent stuff BTW) is now intending to add the 450b to their loaded ammunition line, which is great news indeed. However, they seem to be stalled by the apparent lack of brass available on the market. (Sound familiar?)
I PM'd WildCatter about this problem today, but if anyone else has dealt with a brass manufacturer, any information or ideas would be appreciated. You'd think that a commercial ammo business could attract some interest with a tens-of-thousands (or larger) brass order, but apparently its a problem for some reason.
Off subject: For those who don't roll your own, Underwood Ammo is top quality stuff at totally reasonable prices...you should give them a try!
https://www.underwoodammo.com/