While there are stock axles that are close to the measurements you mentioned, there is not one that's an exact match to the existing axle on your Harbor Freight trailer; in order to get an exact match you'll need to special order a replacement from a local axle dealer.
With that said, if you wanted to do some welding, the CE Smith Trailer Axle w/ Idler Hubs - EZ Lube Spindles - 5 on 4-1/2 - 57-1/2" Long - 1.8K # CE33201GA-HUB could be made to work if you remove and re-tack the spring... view full answer...