Aside from paying premium for them, and solely for the purpose of study I noticed these are generally hard to find on the internet. Anime is popular in the west, so you can readily find this, and Japanese cinema is also relatively popular, so you can find these too.

Popular western movies dubbed into Japanese is a bit of a different story though.

FC2 is the place to go for me. I have a premium account and it's expensive but I think it's worth it.