They're all over the f10 map.
You can generally find 2 ndbs by all airfields. They have a cluster of dots pattern and usually are something like 360 MHz or whatever.
You can put 2 and flip between them on the radio compass panel to your left. Theres two dials to input the frequency of beacons. Change the dial to comp. The skinny needle with a number one will swing to the beacon on your compass. It can bounce around a little in flight but steadies out.
It doesn't have a range so you need to keep an eye on it.
