Congrats on a great find!
Post some pics & a report when you can.
I've never had one of those but the chart says they were made (only) in 1995 & I'm pretty sure all the 3rd Gen's that ultimately ended up with dual nested recoil springs had done so by then. So unless your gun was converted, from single to dual springs, that sounds right that it has the dual.
The one box end label that I saw, also a KPC01xx made in Apr-1995, said
Model No. was
4006. Does yours say that too?
Those two PNs, 108670000 & 108660000 are correct. S&W had some not long ago so you might get them there.
Sprinco started making replacement springs for them a while back.
They're near the bottom of this page:
Tactical Springs & Machine Gunners Lube
.
If you're interest in using a single flatwire spring, instead of the dual nested, take a look at these threads:
4516-2 Spare Springs Source?
BMCM tested and approved 4516-2 springs
Concerns with my "new" 4516-1 (advice needed)
.