The Rankin/Bass Return of the King movie is a Animated TV movie from the 1980 based on the Tolkien book. It is often grouped with the Bakshi Lord of the Rings and Rankin/Bass Return of the King movie as a trilogy, however it has nothing to connect it to the Bakshi movie apart from being animated and being made around the same time.
As it was only a TV movie there were not a lot of collectables produced, however this Theme post details what I have found.
This blog is all about the Rankin/Bass production company and includes quite a bit of detail about the Return of the King movie https://taint-the-meat.com/2013/11/19/the-return-of-the-king/
Here is an article about the artists who created the animation, along with the Hobbit https://tolkiencourse.blogspot.com/p/the-artists-of-rankin-bass-hobbit.html the article also has a link to the artists Facebook directory showing concept art https://www.facebook.com/media/set/?set=a.10151186803695254.794040.349242380253&type=3
The following are websites which feature the Return of the King movie:
Animation Cells
There are a lot of these.
Examples
Tape
VHS
Record
Soundtrack
Rankin Bass Return of the King Movie
Talking Book
