Your search for "spring replacement kit" revealed the following:
How to Measure Trailer Leaf Springs — and Know What Else Needs Replacing
A trailer leaf spring can look “close enough” and still be the wrong replacement. Correct fitment depends on more than axle capacity. You need to identify the spring style, free length, width, leaf count, capacity, eye/bushing size, and the suspension hardware around it. Measure the suspension before ordering — and...
How to Replace a Trailer Hub, Bearings & Grease Seal
Replacing a trailer hub is straightforward when the spindle is in good condition and the replacement hub actually matches it. The work itself is only half the job. The other half is correctly identifying the bearings, grease seal, bolt pattern, spindle family, hub type, and brake configuration before the old...