I actually talked to the shows original creator (Brian Cosgrove?) about doing Danger Mouse shirts, mousepads, posters, and such several years ago. Sadly, Thames Televison owned the rights at the time and he wasn't in any position to authorize DangerMouse products. He is the nicest person from the UK I ever met.
As for the DVD...
It has actually been on DVD in the UK for a while now. Quite frankly, I can't believe it took this long for it to come out in the states. Having seen some of the UK release, I have to admit that some of the episodes look awful and they can't do much since the only archives of those particular episodes are in poor shape. Some of the quirky british humor still holds up today very well though.