Is there a source of Card Katas out there for practice on handling and making techniques smoother? Or does anyone have any practice routines they would like to share?

The shortest (useful) one I have done is Elmsl*y, Jord*n, Elmsl*y, Jord*n,...

I've done a lot of Kata with flourishing but all based on my own repertoire.

-Mary Mowder

You don't need sources. You make up your own katas with techniques you know and use and incorporate moves you want to learn.

So, a card control kata could go like this: Stick a card in the middle of the deck, establish a break above it, shuffle or cut it to the top. Overhand shuffle the card to the bottom and do a transfer cut to bring it back to the top. Perform a double lift to show an indifferent card. Palm the top card and produce it from your pocket. Top change the card, stick the indifferent card in the middle of the deck and use Ed Marlo's misdirection palm to produce the card from the pocket again. And so on and so forth.

It's not difficult to construct your own katas. Just do it.

Just make ROUTINES as Katas. Get the rudimentary moves for an effect or routine and keep working through all movements from start-to-end. Katas are not just a flurry of similar moves. Real Katas have real-world combinations that give you the right muscle memory to be useful like a reflex.
Marital Art Katas (Routines) take individual moves (Sleights) and compliment them for real-world use.
Bad Coin Kata: French Drop, Retention Vanish, Spider Vanish, Back Clip, Coin Roll...blah blah random moves for no reason.
Good Coin Kata: Retention Vanish, retain a fingertip rest, Move to Classic Palm, Kapps Subtlety gesture, let it drop to Finger Palm, Gesture with Ramsey Subtlety.
Then, when you are in real-time with real people your body will do what is needed for the situation.
Watch Masters like Gregory Wilson, he has done this so efficiently that he does improv magic off script to jazz routines because he knows how to seamlessly blends the moves in Katas that automatically flows like music.
Have Fun working on Katas!