Cat scales are all over the country:
There are at least two within a 15 mile drive from my home.
Pull up on the scales, press the intercom button, and drive off (Typically the attendant will give you a "ok pull ahead"). You then park in the lot and pick up your results at the counter (after paying the $15 fee).
Look at that they have a "How to weigh" section on their website:
Then you get a fancy report:
Note that they only give you the weights per axle--no left/right info.