I suggest using the quality joe perk. Also certain containers have certain rare items. For instance my friends use to pass up toilets. Until one day I found a high level pistol stashed in a toilet. Also make sure to empty any containers so they refill in the future. But honestly it just depends what you want.
Augers and chainsaws are usually at the hardware store.
Guns/ parts are usually at shotgun messiah.
Schematics are usually at the book store.
The hospital has tons of medical gear.
If you have big balls and want landmines/ weapons go to the military base.
If you want decent random gear go to the desert and look around for random backpacks lying around.
And most importantly. If you cant find it or make it, you can always buy it