Hmm ... you are asking for *total* removal, which probably needs
a chemical attack. And the solder wets the nickel very well, to make it
more complex.
For a first pass (perhaps to make the chemical pass whatever it
is more efficient) there are various mechanical and tricky ways to do it.
Are these used pins with solder and wire fragments in them?
Onews with the wire fragments removed but lots of solder, or ones which
were solder-tinned from the factory. I'll assume below that it is the
middle ground above, and what I am offering will leave you somewhat
close to the factory-tinned level.
For just a few, without a solder cup for wire ends, I would grip
them in a solder-free area with needle nose pliers or the like, dip in
rosin flux and then in a solder pot to get it up to the melting point,
and then strike the hinge part of the pliers against a wood block, thus
flicking off *most* of the solder (but not all).
With solder cups, what I would do is grip it in some kind of pin
vise, and then heat with a soldering iron and either use a vacuum solder
removal iron or use small braid soaked in rosin flux to wick up as much
solder as possible.
For quantities greater than your couple of hundred, the
mechanical method could be a vibratory feeder to an automated pin vise
Perhaps load a half dozen or more in arms fixed to a common hub, hit
with a hot air flow and while hot, spin the hub so the solder at the
outer ends is flipped off and collects as a film on the inside of the
splash shield, and then hit with a blast of cold air before dropping
them into a hopper.
And probably OSHA will consider it a hazmat zone by the time you
have all that oh so deadly lead mixed with tin scattered all over.
But -- this still leaves you with needing a chemical method.
For the quantities you are talking about, it may still be less expensive
to simply buy new ones with the desired gold plating.
The cleaning methods I listed above would not be commercially
cost-effective. they are what a hobby user would do to clean terminals
stripped from old equipment for re-use.
Good Luck,
DoN.