Try a passport wallet. They would be big enough.
I like the wallets by All-ett, and they have a passport sized one that is about 4 inches by 5 inches. I use their regular wallet but it is just about 1/2 inch too small in the length of a 3 x 5 card. I like their nylon wallets because they have minimal bulk.
If you search for "passport wallet" on amazon you get many to choose from.
Also, day-timers makes wallets (they call them covers) that would hold cards. They have a wide range of prices from $25 up.