Jambe Davdar put an awful life of time and research into his project. He asked around and found a lot of stuff. I don't know of a specific place where you can find the sources of the Jabba scene, but the first post of his Star Wars Begins thread gives insight to all his sources:

http://originaltrilogy.com/forum/topic.cfm/Star-Wars-Begins-Youtube-PAL-NTSC-Versions-Released/topic/7307/

You can write him a personal message asking him, and he might be able to give you more information. That's about the best most of us can offer.