I got mine on-line.

Right now, I live at 4000' above sea level and so I wanted one that was calibrated for high altitude (3000' to 7000' above sea level).

At the ranch I got one that was calibrated for low altitude given that it is only 1900' above sea level out there.

Here's the link: http://www.sciencecompany.com/barometric/barometer.htm