For short clips, https://gelbooru.com/index.php?page=post&s=list&tags=loli+video , https://iwara.tv - it broke

As for half-an-hour long, hand-drawn, Japanese-produced industry-level OVAs, I dunno. Maybe just try google/ddg'ing "watch hentai online". I don't watch them, as picture quality tend to be very low compared to the usual night anime and there's unavoidable mosaics and it's just about VAGINAl, fellatio practices and other such uninteresting things. My guess is that they're just afraid of making truly realistic loli romance plot, or it may be even forbidden by law nowadays, but it's so simple to make it degrade to a mere "meet & fuk" as if it was that easy.