
Next you have to advance the Alvin (quest) to the point where the Gambling Ghost appears and you must win the game against him. So the only way to unlock all 3 Sharpers is to talk to Dendalion and Chireadan about dice but not play with either, although in the latters case you will be forced into the match screen but you can just leave the game before placing any bet, however Chireadan will consider this your loss and talk about how it seems you let him win from now on.
If you played with Koster in Chapter III and left Alvin with Triss, then you only need 2 more opponents to advance to Legend and the Gambling Ghost will count double for advancing the quest as first you have to play him for custody over Alvin.
Sharper Players are a whole different story as they can be hard to unlock as opponents depending on your decisions in Chapter III. Tobias and Julian however can only be played if you don't reach Sharper rank in chapter III, however this in turn will prevent you to play with Koster. Velerad can be missed due to the fact you need to complete Gold Rush before you can play with him and at that point you may already reach the Sharper rank. WITCHER POKER DICE SET PROFESSIONAL
Professional Players that are most easy to miss are Velerad, Tobias Hoffman and Julian.Even so it is not possible to unlock all potential opponents so you will always miss someone one way or the other.
However this can be avoided by first unlocking all possible opponents before playing them, because once unlocked they will remain available even after you advance past their rank.
Advancing this quest will cause some potential opponents to be unavailable due to your rank being higher than theirs. If Geralt fails to learn about dice poker from Zoltan, he gets a second chance while in prison where he can talk to the elven convict. In order to do so, Geralt needs to start from the bottom of the "food chain": beat three novice players, then four professional, then three sharpers before reaching the top of the food chain, the king. The ultimate goal is to beat King Foltest, a legendary poker player. He asks Zoltan about them and the dwarf teaches him the basics of dice poker. Once they have been taken care of our hero finds the curious boxes on the corpses of the recently deceased ruffians. As the witcher is making his way through the village, he comes upon some bandits who are harassing a dwarf, Zoltan. Geralt finds his first starter box of dice just outside Haren Brogg's place in the Outskirts, in Chapter I.