With so many outside the US buying Kestrel Meters, and with Nielsen Kellerman, the manufacturer, located here in the US, the question of where to get them calibrated has come up....

Here's the response from Nielsen Kellerman:

NK aren't the only ones who calibrate/certify (many customers send their Kestrels to local labs for wind speed - and other - tests.  However, I think it generally depends on the service being performed and what the customer is looking to get.  If the customer is looking to validate their unit and prove to a governing body that their unit is within spec, many people send their Kestrels to local labs for this type of verification.  However, if they are looking to actually change the calibration (the former and latter descriptions are often both described as calibration, although I don’t consider them equal for obvious reasons), then very few labs do this unless they’re using the NK RH calibration kit.

We don’t know of many (if any) calibration labs outside of the US who perform recalibrations.  The only labs of which we're aware simply perform tests and provide certificates indicating the pass/fail results of the test.

For information on how often you need to calibrate or to purchase a Calibration kit, check out this manual.