It took me forever to start finding them, but I can get one within a few mins of spawning now. Have you been using a map?
Balota is a good place to get a starting gun, in the "ATC Tower" there: http://dayzdb.com/map#4.049.128
Or any of the big cities, they have tons of spots that can spawn them, especially supermarkets. Barns are decent too if you don't want to go into a city.