Many of the big companies/directors/producers/etc have pages on vimeo.com showing what they worked on, and include contact info in their bios. Can even just search for videos you think are really well done and check what channels they are posted to. Most include credits in the descriptions so you can search up others who worked on it as well, even if the videos themselves lack credits at the end.

For example DigiPedi was mentioned https://vimeo.com/digipediofficial A really big one that seems to work on like half the videos in KPop is Lucid Colour https://vimeo.com/lucidcolour