May 2015 - last edited May 2015
I've been running around from one 'Short List' merchant to another trying to get this armor schematic. I usually start from the Western Approaches. I run around, return to WA, save, exit, repeat. I have 2 Yavanalis staves (random items needing the Short List perk) but not this schematic. I figure if the staff showed up twice then the schematics should have shown up at least once. I conservatively estimate a minimum of 30 repetitions at different times over the course of two days. Which means some of my exits included shutting down the game and my computer.
If you need it here's my system info: system info on hastebin
At this point I'm not going to spend a lot more time on this apparently fruitless quest. I would like to know for future games if it really is fruitless. Thank you.
Never mind. I saw what somebody else did, tried it and it worked in just a few attempts. After getting short list perk, go to Hissing Wastes Merchant. Go back to Skyhold, save, exit and quit the game. Start up again and repeat. Unlike the first method I used, every time I saw a different special item/schematic.