I did some research on this a while back and found that while the US never got all of the Droids episodes (they kept re-releasing the same ones over and over!), the UK got EVERY episode on VHS including "The Great Heep". I think the best preservation source would be these copies, unless anyone knows of anything better.

Regarding Ewoks, I think it's the same story between the US/UK, but I didn't have as much interest in researching that. Still, I think they should also be preserved the same way. I feel fairly sure that Lucasfilm will get around to releasing the complete series for both on DVD, but I can almost guarantee that it will be in a somewhat altered form that's not what originally aired.

--SKot