Laurana Newell kindly sent out word that HKM is making and selling prim breasts. They have a vendor at Wesh Beauties. I have yet to knowingly see anyone with them on, and it will be a bit before I can afford to buy and try out a pair, but I will post what I find out as I find it out.
BTW, while the prim breasts may be new (and I think they are, judging by the bug fixes mentioned on the web site, HKM isn't new to Second Life. I've purchased another item they make, called "Boob Tops Maser [sic] v2", though microwaves are not involved as far as I can tell. It looks like it's intended to make it easy to create tops for prim breasts, but the documentation suffers greatly from very definitely not being written in the author's native language.