Lowering block from Autozone work on the rear. I usually get new u-bolts made as the ones from Autozone are too big and require some redrilling off the sping perches. But not hard to do if you want to do it.
A few years ago I found U-bolts in a variety of width, diameter, and length at 4 X 4 truck stores. I think they were made by Suspension Techniques Offroad truckers use blocks to raise the suspension. The instructions usually say not to piecemeal a suspension together with separate parts (as opposed to buying a lift kit) but I figure if they are strong enough for offroading in a 2 ton truck, they should be strong enough for our little cars.