I engineered one myself, but as far as I know, dangerdan has one. Try some online overclocker dealers. I always looked in the reviews which are archived on the homepage of overclockers. Look in the watercooling topic, there are quite some K7 waterblocks reviewed. Succes in finding one!
I'll also be looking for one sooner or later. I want to get a DD Maze 2 but I dont really have the money right now. I'll be ordering an Asus A7A 266 & 1.2gig T-Bird on tuesday. I'm gonna try and rig my PIII waterblock I have right now to the cpu untill I get some extra cash to get the Maze 2.
Normally would'nt be a problem but my wife couldnt work the last few weeks due to complications with the pregnency. So she got no paycheck! Gotta tighten the belt a little bit ya know.
I've found some sites that are selling Slot A Water Block, but I'm looking for a WB that goes directly on the Core and Cache Chips using spacers for better contact (as I've taken of the CPU plastic box and heatplate, and don't feel like putting back the heatplate).