The Green Hornet is not public domain apparently, but it is available at various websites. As for Batman, this show is the only one. They tried to spin Batman off in his own series in 43, but it never made air; The script for that does exist but that's as far as it went. Other than that, we have this episode which never aired and no others were completed. You'll see some people try to pass off episodes of The Adventures of Superman as a Batman series, but don't let them fool you.

Half a story told by Bruce Wayne & Robin (so much for alter-egos).