Seriously I have the worst luck with finding implements to dispatch the dead with and its so frustrating, I've been to air hangers, towns, and those little shack things in the woods and NOTHING! I find ammo but no guns in sight, I have food and bandages but again NO WEAPONS. Even those axes lodged in tree stumps, can I at least take one of those?
look for weapons in following landmarks: barns, tents, military camps, hangars, firestations and churches.
Barns contain thing like shotguns, winchester rifle and sometime a scoped hunting rifle.
Automatic weapon can be found in military areas (camps and airfields) and firestations but i would avoid most of them, there are many bandits like me that hunt around these areas.
You can find some weapons in other buildings like houses, shacks and other common buildings but chance is much smaller. Not to metion the quality of the loot, you will be lucky if you find a makarov with 2 mags.