I got lucky and there is a vendor at our local reptile show that sells siklworms (but they're a dozen for $5 or $6). He gives you a little bit of the silkworm chow, but it's only enough to last 2-3 days. So I had to feed them out by then. Beautifuldragons.com is supposed to start selling frozen silkies soon. With one lizard (whose primary diet is not meat) I don't think that I could go through a large quantity from Mulberry Farms before they spin (which I believe I was told on another forum that it would be at about 3-4 weeks of age).
http://www.beautifuldragons.com/