As mentioned earlier, just contact forklift service centers. I was looking for a ready-made set of pallet forks to fit my Deere 522 FEL mounted on my little 5303 tractor, and the price was $950 to $1000. I found a service center that had what I wanted- the carriage (the frame that the forks hang and slide on), 36" tall back rest (to keep things from falling over the back onto the tractor hood), and a set of 60" (yes, 5 feet long- don't need that long, but....) 4000# forks, all for $350.
I picked them up a week ago, made my own quick attach brackets, welded them to the carriage, and now the assembly is hanging on the loader ready to go. Too cold to paint, so that'll be a spring job.
I had to call several service centers in bigger towns with industry. They all said that these things are in demand. And they only sell forks that will pass testing- liability issues. I've got a total of $450 in the thing, counting the steel for the quick attach.
Not sure what you're mounting yours to, but I wanted mine to be heavier duty than loader capacity rating.