I should stress that the majority of known recordings are on VHS, mainly recorded off-air at the time of the original broadcasts, and are not all of good quality. They're all watchable, but in many cases that's about all you can say for them. None of them are even close to being suitable for a commercial DVD release, but they're better than nothing.
There are 12 broadcast-quality episodes available on DVD, and the BFI have a further 17 which I am informed are broadcast-quality and hence suitable for a DVD release. I don't know whether Henson have copies of these latter tapes, or are even aware of their existence. Beyond that the only hope is that the original mastertapes have survived somewhere.