I've seen several third editions pop up on
ebay the past few months, it just takes some luck to get one. I'd also check with some of those numismatic book dealers too, since they may have an old 3rd edition in the back room that isn't listed on their website. One of my "mentors" for early halves was really, really nice and gave me a copy of the third edition, but I know that he bought it from
ebay.
Benji- you could always try buying the fourth edition and printing off a copy of the errata if you really need an overton book. I'd also print off a copy of the BHNC's latest rarity revisions no matter which copy you ultimately get. The third edition is 17 years old, and the fourth edition has a LOT of mistakes when it comes to rarity ratings. I'll get that link too, if anybody out there wants it.
On a semi-related note, Ed Souders has reprinted the 2nd edition of Bust Half Fever. He's accepting orders now, and it's around $85 shipped. I've heard that it's an excellent book, and my copy's in the mail!