Here is a personal loot table showing the results of my findings of a gold weapon in-game. Please note I played with the loot tables to make that .1% into 30% so make it easier on myself:
Biters (walker zombies) 0 Gold Weapons out of 258 Zombies Virals (Runners) 0 Gold Weapons After 180 Zombies Spitters 0 Gold Weapons after 120 Zombies Screamers 0 Gold Weapons after 52 Kills Goons 12 Gold weapons after 112 kills Demonishers 17 Gold weapons After NPCs (Rais guys) 0 Gold Weapons Found Shops 1 Vendor sold a Gold weapon (Very ODD) Containers (non-locked) 0 found Containers (easy locks) 0 Found Containers (medium locks) 2 Found Containers (hard locks) 8 Found Containers (very-hard locks) 23 Found Vans (non-locked) 0 Found Vans (easy-medium) 0 Found Police Vans 32 Found Bags (non locked and easy loot) 1 Found Lockers (very hard locks) 5 Found