They definitely have at least some of the UK-shot postcards, as they turned up on one of the US DVD boxsets. A clip from a lighthouse scene also featured.
When the first UK DVDs came out only 12 episodes were included. We were told that these were the only one which could be found; the others were missing presumed destroyed. Happily this isn't quite the case - another 17 exist at the BFI, but I don't know whether Henson are aware of these. It's also quite possible that all the episodes exist somewhere in the ex-TVS archive, which is now in the possession of Disney, but as the paperwork was lost some time ago we will never know unless and until someone is able to catalog the tapes.
I'm not on Twitter, so I'll send you a message via the forum.