Here are a couple of weblinks with a Quicklook at minimum towed vehicle weights without brakes.
Not sure how serious each state is about enforcement, but as has been said "Ignorance of the law doesn't let you ignore the ticket".
It really does help to know just how bad we are "flaunting" the law, and the consequences of getting caught.
State and Province Towing Laws
Towing Laws | BrakeBuddy - Braking systems for motorhomes towing a vehicle
And of course, each state DMV dept has the number buried in their system somewhere. You just may have to spend the better part of the day searching their website for it.