Look on the internet for calibration labs...in SW PA you should find several in the Pittsburgh area.
However, you can use a known good torque wrench to tighten a fastener to...say 50% of your beam scale. Then, you loosen the fastener with your wrench. If the indicator drops suddenly when you reach the torque value you set with another wrench (thus, breaking the fastener loose) you can have a reasonably good idea of the accuracy. Remember, torque settings are to prevent correct tightening of a fastener...and to ensure the fastener is not overtightened.
You might find an automotive repair center that has a torque tester in your area.
Even if you send it out for calibration, it shouldn't cost more then $15 just for calibration. Repair, if required, may not be cost effective.