I'm having trouble on the sound of playing cards, actual playing cards aren't doing it and there are not many resources out there for playing card noises. Any suggestions?
One of the truism's of Foley seems to be that things of the right size and shape seldom sound like the right size and shape!
As Stavrossound said, try different sizes and thicknesses of paper and cards to get the right tonality for the scene. In addition to his suggestions, I'd also suggest index cards, or even try old floppy disks if you can find them (I have literally a bag FULL that has been used for all sorts of interesting sounds).
Business Cards? Post-It Notes? Credit/plastic cards? These are just some ideas, but it also depends upon the action required. Break away from the literal sound playing cards make and think of textures and frequency variances. All the above props offer different tonality, brittleness, frequency characteristics. It's the juxtaposing of various carefully-chosen frequencies which create a sound full of depth and character, whether it be playing cards or any other sound.
An example: A door fx edit can sometimes contain as little 2 to as many as 10 sound elements (or more for a tech door or something)... but each element imparts a different quality which ends up having a balance of high, mid, low (or maybe latch, thud, boom, creak, seal, etc)... the gestalt is a textured, character door with a lot of colorful depth and complexity.
Think outside the box!
I don't know what it is you don't like with what you got, but don't forget all decks sound and act differently, and that different microphone-techniques gives different results! Myself I found a good sound in especially two decks, one Star Wars and one Pondus (a Norwegian comicbook character), recorded with a special tilt on the mic.
The cards need to be new, fresh out of the pack. Go to a gaming store and ask for the stiffest, thickest pack that they sell. Then record with an omni mic almost touching the cards, so that you hear the subtle sounds that the fingers make as well as the cards. The omni is so that all of the sound is on axis, the mic is also not prone to the proximity effect, so will still have a balanced frequency response when working really close.
Here is a link to a video by David Steinwedel recording some sounds for a card game. If I recall the plastic playing cards created a pretty good sound.