Craig Sawyer has made a home brew 7xxx flexible extender a year or so ago. He has uploaded details onto his server, and he says you are welcome to download it.
Notes
I'm not prepared to answer any deep questions about this - if you are interested in a roll-your-own simply adapt as necessary to make something that works.
And posted on October 23 2004:
The flexible one can be made with a scrap frame, a circuit board, some ribbon cable, four lengths of heavy wire an six coaxes (Tek's ribbon had all of this incorporated in the ribbon itself).
The female end can be either a connector from a scrap 7000-series backplane, or a 0.1 pitch, 40-way double sided edge connector. These are available from Farnell/Newark, part number 965-996.
You pull out the end connector pins and insert a pair of 972-216 location keys.
These make the connector locate perfectly on the end of a 7000-series plug-in.
These are in fact ?McMurdo parts; here is the datasheet if you want to find them elsewhere than Farnell:
http://www.farnell.com/datasheets/11753.pdf
There really is shed loads of stuff - and by no means all from me. I can't understand why there is a problem using the search engine on the Yahoo Tekscopes site…
Craig