chaksterI have to agree the low output top MM's of the day are special and getting harder to come by.
The lowest output (0.6 mv) MM cartridge is Stanton 980LSZ
A family relative of your Stanton 980LSZ is the Pickering XLZ-7500 and one I recently purchased with a very low output of .33 mv
and 3 ohm rating.
Another interesting Pickering is the XSV-5000 although not a super
low output at 3.8 mv a very nice sounding cartridge with
a similar stylus.