The battery is a 3V lithium unit, the old one I found is a Sanyo CR14250SE.
Did the fixed I/O SLC's use a spring holder or a wire and plug like the current SLC's do ?
The A-B price is $71 from my dealer.. pretty steep unless you have to mess around a long time finding and soldering on a plug (I'm not eager to heat up lithium cells with my iron).
A quick Google search didn't turn up any easy online vendors, so good luck down at Battery World. If you turn up a good cross-reference to Panasonic or another vendor let us know.