I don't really tend to look at dlsite anime, but I think the principle holds out, just that for video files it's a VJ code instead? I just tried it for a couple of frontpage items and it seems to work for finding stuff related to item you want. Other than that, searching the japanese title of something
can help you find it if that's not working, but requires way more knowledge of Japanese to sort through all the vendors to find sites where people are torrenting or whatever
Depends if the OVA you're looking for is popular, I guess, and who it's popular with. Some of the smaller BL titles I've tried to find are a nightmare, because pirate groups can be pretty bro-y, for example.