Also a problem for me. Wasn't able to get the card due to the first game being un-winnable (bug related), so forfeited the game and the card at the very start. Was pleased to hear that it was patched to show up under the merchant's corpse at Hanged Man's Tree, but was disappointed to find only a book when I checked.
Could someone from CDPR please confirm if this will be patched for 1.07? I am only this one card away from achieving the trophy, so would be nice to get some closure
Also, while I'm on the subject of Gwent cards, I've checked the guides and apparently I should be carrying 3 of each of the weather cards when the cards have stopped being awarded for winning games against merchants and other vendors. I only have two however of the clear weather and torrential rain and I only receive money or random items for winning... Does this mean the quest of collect them all is also bugged and unobtainable?
EDIT: My mistake, just checked the guide again and those weather cards no longer exist!