I just lowered my 91 LX and I ran into alot of problems finding springs too. I used B&G springs, from autoanything.com or amazon.com. $187 for the set!!! Awesome deal, 1.6" drop looks great!
I just need to replace all my struts now, the OEM shocks weren't made for lowering! So make sure you get some good shocks too.. I've ordered some Tokico's for mine...
'91 LX - Faded Silver
Rebuilt motor, B&G Lowering springs, 16" Rims, Walker free flow cat, p/w, p/l, driving lights, sound sys, keyless entry and alarm, All wheel Disc brakes, K&N Filter - All done myself - 330,000kms!
2004 Nissan Xterra Supercharged