Check with a truck company, they'll know because working commercial trucks are always needing springs. We have a big spring shop here in NH that specializes in heavy commercial, but the also have everything for little trucks too. I just walked in the other day and got u-bolts for lifting the front of my D60, they had them right on a shelf. Bought some heavy duty 3/4 ton rear springs there too, years ago.
Just curious, why do you want to stay away from airbags? I absolutely love mine. I wrecked my rear springs hauling sand, and while I always wanted airbags, I figured I couldn't afford to do both. Somebody told me to leave the springs (they're saggy, not broke) and just add the airbags, claimed they did it on an old Ford and it worked great for years. So I tried it, bought a set of 5000# Arnott airbags off Ebay, same as Firestone and Airlift kits only cheaper. Paid about $225, then I ended up buying an onboard compressor from JC Whitney for another $100. I have been very very happy with the system, it rides nice empty with about 20-30# in it, I tow my camper off the receiver with 1100# tongue weight and never get over 40#. Overloaded with winter sand, 4-6k on it, I've only ever needed 60#. Goes up to 100.
Anyway, sorry about going so far off topic. I love my airbags and love telling people about them.