There should be 2 large seat adjuster springs on each side of the frame
With so many people installing bucket seats in these trucks you'd think there's be a glut of original seat hardware around. Unfortunately I think most people throw away the old stuff.
I too have had good luck finding things in a well stocked Ace Hardware. They even had a set of hood springs identical to those in my '56 Cadillac for $10.00. The resto shops sell them for $100.
Take KL Hanson's measurements and look for something close. Note the hooks on each end in my photos. There they are laying on the floor after I pulled the seat.