I have a 1988 Playhouse Video VHS of the film and it shows that Playhouse Video is a Division of CBS/FOX. Interestingly, 20th Century Fox Video (founded in 1995) encompassed CBS/FOX. Then in 2000 CBS merged with Viacom - at which point CBS/FOX ceased to exist. (I'm thinking out loud here, bear with me...)
At that time, CBS/FOX still owned some ancillary rights to certain films (unrelated) until 20th Century Fox fully assumed CBS/FOX's share of them. So Viacom kept nothing, Fox kept everything. Another interesting point is that the BBC license with CBS/FOX also ended in 2000, where Warner Home Video took over.
According to the Warner Home Video Wiki - they acquired MGM/UA, Pathe Communications Corp., Turner Broadcasting, Turner Home Ent., PBS Home Video, New Line Home Video (aka New Line Home Ent.), and HBO Home Ent.
"In 2009, Warner Home Video introduced the Warner Archive Collection, which allows the public to order custom-made DVDs of rarely seen films and TV series from the Warner and Turner libraries."
The VHS I have says Fox Video, so 20th Century Fox or Warner Bros. may contain the rights. Forgive me if you've already gone over all of this. I'm excited at the prospect of solving this mystery and getting the show on the road, as it were.
I will continue to dig a bit more and, if time permits, perhaps make some phone calls.
For some reason, every time I've seen this film, I have thought it was originally Canadian, as it displayed many of the animation tropes and techniques used in other Canadian films of that era (e.g. the Care Bears films released by Nelvana).
Garrett, it's encouraging that neither you nor your compatriots are giving up on this endeavor. Keep up the fight! I'll keep you posted as things come up.