This is where things start to get a bit tougher. The following cards can only be acquired by completing Gwent-specific quests, which means you will have to defeat much tougher opponents with stronger decks.
Tibor Eggebracht is one of Nilfgaard's famous heroes, and has a ranged attack value of 10. He will be the first hero card you obtain for this powerful faction and will basically be a wolf among sheep compared to your other cards this early in your Gwent career.
Eggebracht can be won very early on. You win him from Olivier in the Kingfisher Inn in Novigrad, as part of the Gwent: Playing Innkeepers questline. Unfortunately, you will have to collect more standard cards for Nilfgaard before you can actually utilize him, but for anyone playing this faction, he is an obvious inclusion.