You can get the apex springs from carparts4less using the 10% off performance parts code displayed on the website for £100 new delivered which is the cheapest.
You're looking at a wait of at least 3 weeks when ordering brand new due to them being an uncommon part. I have Spax springs on mine (lowers 30mm on the front & 25mm on the rear) and got them for £130 from Larkspeed, took about 3 weeks to come.