Where do you find good armor in Guild Wars?

no you can not

Improved AnswerYes, players can trade armor with other players. However, every piece of armor is customized to the original owner, and can only be used by the character to which it is customized. Because it is customized to the original owner, it cannot be use by other players.

So, while yes, armor can be traded between players, there is very little reason in doing so as it is customized to the original owner. A piece of equipment customized to another player cannot be worn and is only useful for salvaging materials, runes, insignias, and other such equipment upgrades, or to sell to a merchant for in-game currency. That, or to keep as a keepsake for personal reasons.