Like the coelacanth, these are not quite so extinct as previously thought.

Fronts: 360-580 lbs.
Rears: 168-216 lbs.
Drop: 1.25"

Do a Google search on this part number: KBP-85330

...and you'll find two vendors who carry these springs.

They're being marketed as "Kenny Brown Sport Springs" but they're the same thing. Even the rear isolator part number is the same... UR001.ILR.

Just an FYI in case anybody else out there, like me, was looking for these springs.