On the producer site (Fantasy Flight Games) you will see that you can use their 2 1/2" x 3 1/2" (63.5 x 88 MM) card sleeves.
On this link you can see that you can use 3 packs of their Standard Card Game Sleeves (grey color packs) and on this page you will see the card sleeves sold by them (the last product from the list).
Another card sleeves producer is Mayday Games. I think that their corresponding card sleeves are named "Card Game Sleeves" (2 1/2" x 3 1/2" (63.5 x 88 MM)) - green pack. I am pretty sure but you can visit their site. They have a pdf file where you can search for your game and see what kind of sleeves you need. IMPORTANT: Today I see that their site is consider by google as threat because they find malicious software, so I think is not a good idea to enter wright now on their page.
Also you can search for ultra pro sleeves but i don't know exactly what kind you should search for.