Quality is hit or miss based on the studio but https://vrporn.com has a lot of content.

https://eroscripts.com sometimes has script releases that include a dl link to the video as well.

Otherwise, almost all studio websites give you the option to download short 2 min preview videos in full quality. Go to https://sexlikereal.com (a portal/collection site) to find studios and videos.

Better quality makes a huge difference. Don’t look at anything below your native VR headset resolution if possible.

Xhamster has an vr section

I’m only familiar with JAV (Japanese) content, which sukebei.nyaa.si has quite a bit of. I suggest browsing for what you want on javlibrary.com and then search for a download on nyaa

Well eporner is best, then porntrex. Spankbang used to be the best but they changed something about who can upload so now it’s all ten minutes teasers, but there’s a tonne of stuff still there from before. They all do up to 4k.