My 99 has All-Pro rear springs, but it's a highly modified truck with very few factory suspension parts left on it.
Theres a couple aftermarket vendors selling replacement springs but the problem with most of them is they make the truck ride stiffer, thats why the factory springs have issues.
Toyota had to make a compromise between strength and ride quality.
Always avoid springs that are labled as "Progressive rate springs" which is what is used on almost all TRD model trucks. Progressive rate springs offer a great ride for normal bumps and road conditions, then when the going gets rough and your bouncing the springs harder they get stiffer, but the problem is their subject to more metal fatigue and wear due to the metal make-up and annealing process, so the end result is after a few years they dont have the spring they once did, the metal looses it's memory and the truck suspension starts to sag.
Non-Progressive springs will make for a stiffer ride but result in a longer lasting more durable spring able to take heavier loads.