Looking at the trailer pictures, I don't think that you need to buy new risers. The old ones look perfectly good except for the length. What I would do is use a metal cutoff saw to shorten the originals and a drill press to make new holes on the shortened pieces for the swivel top piece. Easy for me to say because I have access to that stuff. Pulling them off and taking them to a machine shop (pre-arranged to save time), I would guess it will cost 1/10th of buying new.
And that way you could shorten the risers by 1.5 inches, 2.25 inches, whatever is best. It looks like you could go more than 2 inches, but you'll have to measure carefully.
An air wrench sure makes trailer work easier and way faster. Maybe your local grease monkey/mechanic will have that as well. Have the raw cuts/holes sprayed with galvanizing paint ($6 at Home Depot if the shop doesn't have any).
I'd get a bid before ordering new ones.