I agree with Plumpurpleplym - we've got an independent, General Spring Company, here in the KC area and they'll form and heat treat springs based on size and weight needs. There's an Auto Spring Company listed on Range Line in Joplin, too, which is your back yard. Not sure of their capabilities, but I'd give them a look.
Auto Spring CO INC
4600 S Range Line Rd, Joplin, MO 64804
(417) 623-3091