I went to the 325,800 area and found BOTH an adult and mature standing side by side ...
Also, for a mob rated 40-43, this thing tore me up and I had a Khashek's Katar, a Fist of Iron, 31% haste, and a fungi ... had to FD twice to shake of a stonegrabber. Tough fight... mature rockhopper was crazy fast, wish I had a slower with me. ;o)
These things have crazy regen on them too, in the time it took me to heal from 20% hp to 28% hp with the fungi, it had healed from 50% to full health.
Ok this guy definately spawns in the Scarlet Desert. I bought one off some guy who had just killed one and on my way to buy it I saw another one and killed it and got the wire again. He looks exactly like the other rockhoppers there except he's a bit bigger I think, not enough to really notice. Only thing I ever got off of the mighty rockhopper in Mons Letalis were the stupid claws. I'd say just keep searching to the right of the zone from twilight and kill all the regular rockhoppers to get him to spawn.
Not exactly sure how you managed to get "the wire again" as it is a lore item.. perhaps you meant you got the mob, and the coiled steel wire dropped.. but if you had just bought one as you say, then you couldn't mean you looted it and had two at once in your inventory.. right? or maybe the Lore tag is actually an error? doesn't matter. Anywhoo.. I was curious what you payed for the one you bought? as I have yet to see this in bazaar at all.
Ah Nevermind, I found him! (The Mons Letalis one) He spawns in the crevice around loc 325,800. His placeholder is "An Adult Rockhopper" which patrols up and down the crevice. Luckily, it's a teeny tiny crevice and he won't roam far.
The Coiled Steel Wire drops from A Mighty Rock hopper in Scarlet Dessert. (Not Mons Letalis) When you come in from Twilight Sea, just turn right. Between the 2 Sun revenant camps on this side there is a area with wandering mobs. This is the place where i catched him. Good luck to al mz fellow Monk sisters and brothers.