The parts are basically CJ3 parts. Bearings, races, etc. can still be found at NAPA with the right part numbers. Spend some time with Google and you'll find them.
My quick search yielded some sites with:
· Shock Absorbers (2 per trailer):
NAPA 94038 $29 ea.
*this is for a mid 1970's CJ-5 with a 4cyl engine
· Springs:
1950's vintage CJ3A/CJ3B FRONT leaf springs (36.25x1.75 inch leaf springs)
· Spring Eye Bushings:
1950's CJ3A/B Front leaf bushings
· Shackles:
1950's vintage CJ3A/CJ3B shackles.
Note there is a right and a left threaded shackle. You'll need one of each.
Available from JC Whitney or any jeep parts specialist. These are commonly
called "c-shackles"
· U-bolts:
Again, 1950's CJ3A/B U-bolts for a Dana 25 axle. You want the "skinny" u-bolt
as there is also a wide u-bolt to clear the pumpkin on a D25. With nuts, they
run about 3.60 each from Willys Jeep Parts, Restoration & Wiring from Walck's 4 Wheel Drive | Willys CJ2a, CJ5, Willys Truck, Wagon & Jeepster parts
Which might have come from:
https://sites.google.com/site/m416trailerproject/m416faq-html
Good luck!