There’s a great article by Tony DiTerlizzi on the origins of several weird D&D monsters, which began life as cheap Japanese plastic toys. Based on those toys, Gary Gygax made up the Carrion Crawler, Umber Hulk, Rust Monster, and Purple Worm. Tim Kask made up the Bulette. Someone (Tim?) later made up the Owl Bear from a similar figure. I have one of those early rust monsters, but the antennae have fallen off.
Searching for “Japanese monster toy” is a fun way to spend an hour or two. Going to Amazon Japan and shopping for toys is less enjoyable, as there are tons of stupid cheap toys that no one would want, and a lot of soft porn disguised as Japanese anime figures (those folks have issues!). I did find one interesting set at Ali Express, but it was very expensive. There were some new Yu-gi-oh and Amiibo that looked good. There is a really nice set of dragon figures from How to Train a Dragon, and reasonably priced too! Another version is over here.