www.motorsportworld.co.uk will do you a set of AVO lowering springs at a fair price. You might want to upgrade the shocks at the same time as this tho as the standard ones tend to be buggered by now. Monroe do up rated inserts for the fronts and rear. KYB also do some but I'm not sure where to get hold of those. Most local motor factors will be able to quote you for the Monroe's.
For the front,
If you want to go down the coilover route then you can make your own, s13eater did a write up on this not so long back, or, you can fit aftermarket S13 coilovers with some jiggery pokery and parts swapping.
For the Rear,
You can make your own again, there is a link in the write up the s13eater did to club12 where someone did exactly that or you could fabricate new rear towers to hold the S13 aftermarket options. Spax will also make a coilover unit that has an elongated upper shaft that might fit in the standard S12 rear towers, however this, as far as I'm aware, hasn't been tested.
Just search for S12 Coilovers and you should find what you need.
EDIT - Why say 10 words when you can say 100 aye Martin!
