PM him as it was simple and clever and looked like it'd work well. I couldn't find it on his site when I was looking the other day though.
And there's always Swiftech's approach to socket holddowns.
Oh and depending on what block you are using you might be able to use the clip from a Dangerden Maze1C on your block. Or for that matter what about DD's Maze 4 socket hold down:
http://www.dangerden.com/mall/blocks/maze4.asp
Might have to e-mail them to see if they'll sell separately though (or ask Bruce at cooltechnica)