Can't help you with the original specs but, one approach might be to get it unloaded, take it to a scale & get it weighed. Then add 1500 or so lbs to that (cargo or carrying capacity), and then look for a slightly higher rated axle.
It looks like many manufacturers today use axles that are rated near the gross weights of their trailers or even slightly below that. I think if the axle weight
rating is too high, you'll bounce over every bump.