i would say that models with a an original nude body, with nipples and vagina, and available legally are comparatively rare. rare as in, 1 in 10 or less. note that i said original, as in, not a head swap.
and i wasn't addressing the issue of whether or not there are a lot of them; i was saying that the majority of them are not original models but are head swaps with custom girl models or other nude bodies. so, if you're at all capable you'd might as well just head swap yourself in most cases.
but if you're confident there are as many as you say, it'd be kind if you gave some examples. i'm really not that interested myself so i can't offer much besides eto's cirno, which you'd have to ask him for, i think.
for anyone interested in nude models getting 3d custom girl is a good idea.