Sounds like the good old 3-wire low voltage relay control system. Despard 1PdT center-off momentary rocker switches, load relays with low voltage control. It is still available today, but not too commom.
The relays are GE (there are probably others), the switching end goes in the outlet box, the low voltage control end is outside the box. The relay has an open coil and a close coil, both coils share a common return wire so the result is a 3-wire control.
A few years ago we installed some large 277/480 panelboards (GE) which had extra large wireway space which included a bunch of the exact same GE relays, only these relays were controlled by the buildings automation system. It actually was pretty cool.
We have a neighborhood nearby which was largly built in the 40's and these homes commonly have this type of switching. The local Ace Hardware store carries the relays and the switches and gouges badly for them (like $25 for a little despard switch and $50 a GE relay).
If I get time later I'll sketch out a schematic or find a link to more information. Who knows, maybe there is something here in the tech reference area.
There are 10 types of people. Those who know binary, and those who don't.