You will need:
A deck of cards
Step 1: Key Card
You will need a key card on the bottom of the deck. I use nine of hearts but whatever works. You may shuffle as long as it stays on bottom
So say they picked a queen of clubs. (Remember to tell them not to let you see it) after they have memorized the card, Separate the deck into three piles. Ask them to put the card on top of one of the piles.
So whichever pile they decide to put it in, arrange it so your key card (nine of hearts) is on top of their card and pick up the deck.
Now you have your deck. Dispense cards face up from the top in piles that have less than 15 cards In each. Stop when you see nine of hearts ANYWHERE and start a new pile. The fist card on the new pile is their card. Spell out their card on the next pile. Keep going.
Whenever you spell their card, Arrange the cards so that the spelling is on top of their card. Put all the other cards under it. Make sure the key card is o the bottom so you can do it again!
One last step! Ask them what their card was and then spell it out from the top of the deck. Flip the last card over. It's their card!!