I've seen a (very) few Telvanni plans in guild stores on PC-NA, but they were priced ridiculously high - like skooma bubbler plans when they first hit stores.
They're listed in CraftStore and apparently all purple quality, but I've never seen a recipe. Do you suppose we'd have a higher chance finding them in Telvanni areas, or does everywhere on Vvardenfell have the same loot table?
I read somewhere that you get them from pick pocketing Telvanni citizens, similar to how the bubbler was.
I will try it after I get done this hitch. I have like 5 or 6 skooma bubbler plans so it should be no biggy if that is the case, depending on loot table.