They only drop as rares, hence your best chance is from a chest. I've found 2 golds from a chest, but they were pretty crappy (18 while uner 50, 14 while enchanted), so yeah, keep trying.
i found mine from sskai (almost thought his sword dropped but it was a crappy gold jade sword ... +19% while hexed :'()
seeing sskai is naga i suppose wiki is right
Yeah, it's easiest if you want one of them to just open chests and hope for one, since the chance of a gold drop is really small from a monster and the chance of a jade sword is even lower.
my Jade Sword got dropped from a Fungal Wallow (I was chest running outside Zos Shivros, and meanwhile killing all Wallows/Island Guardians, so I would get items/gold to buy more keys).
I killed some Wallows, and a max dmg req 10 Jade Sword dropped ^^ (it turned out to have dmg + 15 (in stance), and no other mods)