This is an interesting comparison between and Earthworks M30 and a Dayton EMM-6 that has a calibration file provided by 3rd party tester Cross Spectrum Labs.
hifizine.com – Dayton EMM-6 measurement microphone, calibrated by Cross-Spectrum Labs
Interested in having a mic tested and being provided with a frequency and polar chart as well as calibration files?
Here is an interesting thread that appears to include comments by Cross Spectrum Labs staff regarding Dayton factory calibration files:
hometheatershack.com – Re:Cross-Spectrum Microphone Calibration Service – USA