Not sure which makles something rare or uncommon but I have been here no less than 6hrs since the revamp- last night 3hrs alone and never saw anything but kelp clothing. If your looking for this or the illusion shawl bring a team and be in for a long wait.
The mermaids drop this down in the water tunnels. Spent the better part of 3 hours farming for the enc/brd illusion shawl for a friend and got one of these.
Put it up on vendor for like 2k and didn't sell for over a week. Dropped it down to 1k I think and it sold. As these other guys posted, there are better items to get.
I would say this drops off the Sirens in SG due to the name. Dunno on the pricing for this item though. You didn't mention your lvl, but if you are looking for an EB item to swap in and out, there are several to choose from that may take time, but won't cost. In Qeynos hills on the lake is a mob that drops an EB earring. Long camp though, and often camped. You can get snake organs from snakes in The Grey or off Taskmaster in Echo and turn in to NPC in Katta for a free EB neck item (if evil, check faction with Katta first). Although this takes time, as long as you are high enough in lvl to fight these, youc an get exp for these mobs.
the Snake organs quest is a very good one, i spent 2 levels in Echo Caverns killing the taskmaster (man, that was forever ago...), he didnt drop the organs very often, BUT the guys in the grey, if you can handle them, you can prolly have all 3 organs in about 45 minutes tops. lemme find a link to the quest in question.
Agreed, Snake Organs is the way to go. Got them for my warrior fast, and then ran my level 30ish cleric over and got him some organs too. Common Common drop and mobs are easily soloed (i did it at 58-60, can't remember, warrior back in 02)