What happened to vamp.jp and is there a way to access its catalogue or even its preview pictures?

I don't know. But if you know the catalogue numbers of any releases that's worth a try.

I've always been able to find Opera AV videos by searching for OPRD-061 for example.

Does anyone have the list of codes from vamp?

Excuse me, I saw this picture of VADV-50 shot by Vamp in your post, I really want to download or purchase this video, but I have not found an effective path, where did you get this picture?Besidesfor Vamp's lotion line, I found VADV-25 37 50 53 56 63

Vamp has been out of business for at least a decade...and "lotion" is a niche interest even in Japan, so good luck finding anything. I've looked.

FYI: Vamp used to use/have a label called "Cobra" that published some of their lotion vids. Using that term might help you in your search. Good luck.