In Guild Wars 2, enemies drop pieces of armor you can wear. The further you get, the higher level the dropped armor will have. But from where (or which locations) do the enemies start dropping pieces of armor with the max stat?
You find max level armor in the max level zones...
That would be the Cursed Shore and Malchor's Leap at the southern end of Orr, Southsun Cove (take the boat from Lion's Arch), and Frostgorge Sound (in the far north).
... and everywhere else.
You can get max level armor in any zone once you're at or near max level (say, 78+). When you fight in areas where you're sidekicked to a lower level, enemies will mostly drop gear appropriate to their level, but will occasionally drop gear appropriate to your true level. Thus, level 80 armor can drop anywhere once you're at or near level 80, though you'll find the drop rate is higher in actual level 80 zones.
But what you're really looking for is exotic level 80 armor.
GW2 armor, as well as having level requirements, also has quality tiers. The tiers are, from lowest to highest:
You can ignore legendary & ascended; legendary quality is for weapons only, and they can only be made by crafting & combining huge quantities of rare components, while ascended quality is only for jewelry, and only acquired with fractal relics from Fractals of the Mists and with laurels from completing daily & monthly categories. Neither of these quality tiers ever just "drops", and they're not available for armor regardless.
Exotic quality equipment, however, does drop. The most reliable way to acquire exotic gear is to get it from bonus chests. When you complete certain events with a character of at least level 40, you get a bonus chest that is guaranteed to contain an item of at least rare quality, though you can only get a bonus chest once per day per event per account. So once you get a bonus chest from event X, you can't get it again from event X on any of your characters until the daily reset, though you can get bonus chests from other events.
Most events do not give a bonus chest; primarily bonus chests are given from world bosses (Shadow Behemoth, the Fire Elemental boss at Thaumanova Reactor, the Dragon lieutenants) and the temple events in Orr.
Besides bonus chests, exotic armor can be acquired by doing dungeons (you can trade in the tokens you get for doing explorable mode) as well as from certain karma vendors in Orr (albeit for astronomical amounts of karma).