There are at least a half dozen threads on the "mining specific cards" on Bitcointalk - some Nvidia specific some AMD at least one for both.
As it happens, I just ordered
https://www.newegg.com/Product/Product.aspx?Item=14-202-292 So at least SOME of the cards mentioned are legit.
It doesn't appear to be AMD and NVidia themselves that are creating the cards - it's partners like Sapphire and ASUS (verified on their own websites and Sapphire has at least *3* cards listed on Newegg), Galax has also shown up in at least one video I think, MSI has at least one that showed up in a video, EVGA and a couple others are rumoured to be getting in as well but I've not seen verified info on those *YET*.