By "semi-retired" I mean a pornstar who made her name doing hardcore (M/F) that has since stopped doing hardcore in favor of lesbian or solo scenes only. So, they're not giving us what we want anymore, but they haven't stopped doing porn, and I would bet some of them would do a scene or two if the price was right, they could pick the director and guy to fuck, maybe no anal, and other conditions. It's something I think some of the higher-end studios should investigate.
My pick would be Sunny Lane -- she did some great scenes years ago, and she seems to still be shooting lesbian stuff.
I'm trying to think of naturally busty girls that are semi-retired -- I know there are a bunch, but I'm drawing a blank.