My rear axle has a slight bend, looking to buy one. Axle is 3/4" x 36" with 3/16" key way 4" at each end, axle is solid 3/4" with 3/4-16 threads, 1 1/2" of threads at each end.
Your kart might have more value in the vintage kart market with its original axle. I'd take it to a good machine shop, they could probably straighten it out good as new at a reasonable cost.
Hey did you ever call Van-K about those front wheels you needed?