Guild Wars 2

T1 cultural weapons are also available as Masterwork (green) drops in areas associated with that culture (e.g. Glyphic weapons can be found in Maguuma zones, such as Metrica Province).

T2 cultural weapons are also available as Rare (yellow) drops in areas associated with that culture (e.g. Aureate weapons can be found in Krytan zones, such as Gendarran Fields).

T3 cultural weapons are mostly unique to the karma vendors, though there are also a few times in the Personal Story where weapons with the same skins as the T3 human Seraph weapons can be selected as rewards.

Cultural armors of all tiers are unique to the armor vendor, there is no other way to get them.

Making Eternity requires Sunrise + Twilight + 5 Crystaline Dust + 1 Skill Point. There’s no added value or difficulty that makes it worth something to buy it pre-crafted instead of just buying Sunrise + Twilight and making it yourself.

In theory, the only way that should sell is if
a) The cost of Sunrise + Twilight is more than 5k for an extended period of time (currently it is 4.5k).
b) There is no Sunrise or Twilight available on the TP for an extended period of time, making it impossible to craft Eternity by buying Twilight and Sunrise separately.
c) Someone with ridiculous amounts of gold who doesn’t know how to craft Eternity buys it.
d) It’s some kind of scheme as Sauzo suggests.

The cost of T+S isn’t that far below the listed Eternity. Its conceivable that it could permanently rise above 5k and make the purchase worth while. It won’t be selling for that reason in the short term, though.