You have probably seen the listing for the foot switch that KHB assembles for those timers, but in case you haven't, here it is - $98.00 CDN plus shipping:
http://store.khbphotografix.com/Footswitch-for-Kearsarge-Darkroom-Timers.html
FWIW, I had KHB make a similar foot switch for an Ilford Multigrade controller/timer (unusual connector) and, while it was expensive, it was of great quality.
I used it for several years, and it was well worth it.
I believe this shows where the connector fits on a similar Kearsage timer: