I found a mother lode of stuff, most of the extras from the 2015 digital-only release of the Star Wars movies are posted here: https://www.youtube.com/c/LEKHANHProductionsLtd/videos

Some of the videos:
Discoveries From Inside: Models & Miniatures
Conversations: The Star Wars That Almost Was
Discoveries From Inside: Hologram & Bloopers
Conversations: Creating A Universe
Discoveries From Inside: Weapons & The First Lightsaber
Conversations: The Lost Interviews
Discoveries From Inside: Matte Paintings Unveiled
Conversations: The Effects
Discoveries From Inside: The Sounds Of Ben Burtt

and much more. Be sure to go through all of them!