It turns out there's an exact method to get 600 gear score in New World, and it's somewhat consistent but takes a lot of time to get there.
See also:
Housing guide: /watch/UE-rFsPoJMKor
Furnishing guide: /watch/8hMAcGtyhiSyA
Skinning cheat: /watch/kpV2wp9sZjts2
Engineering cheat: /watch/sWbqje6ya0yyq
Max level in 3 days video: /watch/YTpmG0PwbH1wm
best and worst job board mission: /watch/0AkQ7CxEr9dEQ
Weaponsmithing guide: /watch/cg5snRXcbGHcs
Armoring Guide: /watch/Ykp8zXaE17wE8
Engineering guide: /watch/ESKz3wkkSTMkz
Jewelcrafting guide: /watch/gQ_4U6DUkw3U4
Arcana guide: /watch/oJrY7OGunUquY
Discord: https://discord.gg/SBQsaQzyM2
Getting the New World max gear score is only possible by grinding like crazy on level 60+ enemies. This is because your hidden gear score can only go up randomly when you find rolls, then you can find higher level stuff.
Alternatively you can get New World 600 gear score before then by crafting the gear instead, but this will require quite a bit of legendary materials.
The fastest way to get gear score in New world is a combination of dungeons and myrkgard castle. You'll need to eliminate hundreds or probably thousands of high level enemies and end game bosses to get your gear score up, and unless you're really lucky, it will take a long time to get the exact gear score you want, even once you increase your average gear score drops.
Now you know how finding higher gear score items works in New World.