I managed to get my hands on the Thunderbirds 1965 Blu-ray on the 'secondary market'.
It cost me quite a bit, but I understand that the producers are going to issue a second, larger batch of Blu-rays, now that the licensing has all been straightened out, for anyone like me, who missed them the first time around.
The Blu-ray contains 3 new shorter episodes; about 25-30mins in length, which are based on the three audio episodes that were released on EP vinyl in 1965 and 1966.
The three Anniversary episodes were made in 2016 by creating the visual elements to accompany the original sound recordings.
Check out the Century 21 Slough documentary as well.