Burton, I second Stainless. I see you live in Wisconsin, so go to your nearest Fire Extinguisher servicing outlet (usually a Safety Apperal store).
As long as you bring in a copy of the sales brochure that shows the "full" Weight or if the bottle shows the "full"weight on it, all they have to do is weigh it and certify that the bottle has been inspected "by weight and appearance" only, meaning that the gauge does not appear to be tampered with.
There is one unscrupulous company that will tell you that the bottles are out of date, or his own filler is no longer good, that the SCTA is a bunch of Asshol*s, and that Jim Deist was the biggest Asshol* of all.
I won't name him but he is in Florida. Bob (AND IF HE WANTS TO ARGUE THE POINT, BRING IT ON...........).