I found all 3 shorts on files on an archive burned DVD-ROM disc I made of old files I downloaded. They were the highest quality ones, 1500kps 480x360 Quicktime. I've posted them to archive.org:
I don't know if any of those are also considered "lost." There's 3 "sneak peek" videos with intros by John Ratzenberger that maybe also aired as interstitials to a Toy Story TV broadcast (2nd sneak peek has Ratzenberger mentioning that "you" the viewer are watching Toy Story). I can't find these online via a quick search, but maybe I missed it.