Here, in Mn, there are a couple different companies that are commercial rated. Felling http://www.felling.com/
MidSota trailers http://midsotamfg.com/  and TowMaster http://towmaster.com/trailers/

These guys will build to your spec's or pic from theirs. I would consider 8000 lb axels and 17.5 load range F commercial tires.
Seems guys are always overloading tandam axel trialers and the DOT will look at tire carring capasity and air pressure if stoopped.
Those mfgs will not have trailers / axles / tires that wear uneven,even if you overloaded.