The idea of varying your frog's diet is an excellent on. Silkworms are just one of the many "new" foods to come onto the market in recent years. You can also feed tomato hornworms, cockroaches, waxworms, butterworms, etc. I don't really remember the policy on posting sites, so just search "silkworm farm" in google. The first result that I got is a well know reptile food source.

Best of Luck,
Alex