yeah man, i've been vendor searching for anything like it and haven't seen anything at all. I kinda figured that if someone actually wanted one of these things they'd have at least said something. I've got 4 different ones now. Not sure how many there are total, but, hey, whatever
This is from the trade quests. If you take your trade order to Slim the Fence instead of to the city it goes to, you have a chance to get forged artwork. They aren't common rewards, but neither are they super rare.