There should be local businesses who can do this for you if there are any manufacturing or assembly firms in your area. For ISO standards most assembly and test equipment has to be calibrated regularly and there are companies that do nothing but equipment/tool calibration.
That said, you can get an idea how close your (click type) wrench is at home. You need a relatively accurate set of bathroom (spring type) scales and a mounted bench vise. Take the bath scales to the workbench and weigh yourself. Write your weight down. Set the torque wrench for the range you're concerned about. Wrap a piece of tape around the torque wrench handle at a place 2 feet from the center of the drive end of the wrench. Clamp the drive end of the wrench in the vise such that you can pull up on the wrench handle. Step on the scale, grab the handle at the tape mark, pull upwards slowly while watching the scale. Note the reading where the click happens. Write that down. Now do the math. Take the scale reading, subtract your weight, multiply by 2 (for the 2-foot tape mark) and that's the actual torque (lb-ft) your wrench "clicked" at. Repeat this several times to get and average you can trust.
This DIY home method will only be as accurate as your bath scales and is obviously subject to errors, but it will tell you if your wrench is close enough to be trusted... or what amount of offset you need to dial in. It's better than using a totally uncalibrated wrench. I use a nice old Craftsman unit that is very accurate. I also inherited a Harbor Freight special and it is NOT accurate nor is it linear. I only keep that one for sentimental reasons.