These are selling for 70kish on Alexander. Was pleasantly surprised to get one drop off the lamia near the Arrapago Reef zone north of Caedarva Mire (main entrance). Of course I must've soloed like 20 of them while skilling up my evasion.
[edit]: So to clarify: I got this drop in Caedarva Mire off a Lamia Fatedealer (corsair kind), just outside the zone you go into for Pup and Cor flag quests. Spawns would vary between decent challenge and even match for a level 75.
To get scintillant ingot on it's regular synth it's 98. I don't think this would be quite this high as a synthing cap, but I am sure you're gonna want 100+ synth support to expect any kind of results from this desynth.