Have you checked with local state/private game fish farms? They may have blackworms in their raceways and settling ponds (they'd call them trout-worms). Of course, worms raised without fish would be safer in terms of disease risk.
Hey Auban, great to see you around again! I've been away from the forum for quite a while also (though certainly not nearly as far away!)
I was just talking about this thread the other day because I've just recently started working at Conservation Fisheries raising native fish, and we go through A LOT of blackworms. However, the drought in California has pretty much shut down production of Blackworms from out that way, and we've had to switch to someone that raises them here in the east, but have not exactly been thrilled by the quality of service. If you find a way to produce these things, I can pretty much promise you there'd be a market for you. And once I get settled here, if I can manage to find a place where I can toy with ponds sometime, I'd love to seed mine with some worms and see how they do. There's a mystery here and someone needs to crack these things so they can be accessible from more than two sources in the entire country