You apparently need an AC-HB1P, but good luck with that, they seem to not come up very often. I've only found a single eBay auction from two years ago, and Amazon actually has one but it's kinda sorta expensive... edit: Buying directly from that Amazon seller's site promises to be much cheaper, but judging by the lead time it's likely to turn out to be unavailable.
Kev, that plug end is the same style as a neo geo CD plug, maybe you can build one from one of those? ( even though those go fro a premium right now too) but must be more common.
Looks like it'd be cheaper to commission one to an electrical engineer if you got the specs of the AC part.
Presumably he wants an AC-HB1 rather than the P version - since it's a pretty safe assumption that the P will be 220V.
You need an AC-HB1. AC-HB1P and AC-HB2P (sold with the hb20) also work, based on their pinout info, but they are 220V. If you build an adaptor, the single top pin is 6V DC, bottom left pin is 16V AC, and bottom right pin is Ground. They pop up on yahoo japan every few months, last one appeared just this month. Ask Yakumo to put it on his watch list for you. http://page4.auctions.yahoo.co.jp/jp/auction/d194993179