blackworms are very hard to culture - alot of "blackworm farms" use trout ponds to raise the blackworms.
They need alot of water, and alot of oxygen.
Its probably easier to just buy them and feed them right to the fish than it is to culture them.
Whiteworms and grindal worms are much easier to culture, and you can probably get starter cultures at a meeting/auction of your local fish club (like the New Hampshire Aquarium Society or Boston Aquarium Society), or order them from ad's you'll find in the back of most aquarium magazines.
I have seen a "new" worm, "micro-fex", that is alledgedly a mini tubifex that can be cultured at home. I tried culturing them, I barely got any food from the culture over a months time, and then it crashed.
(I got mine from a club member who was also trying to culture them).