Mist, sprinkle, etc. some water onto your card-stock. It doesn't take much. Then start wrinkling it up many times in different positions.
Take your opened piece of card-stock and rub it down the edge of a table to flatten it out and let dry.
1. Iron your paper to make flatter but it still leaves the crinkled look to it.
2. put in between towels and stick heavy, flat objects on top of it.
3. Just use the edge of the table end let air dry for a more uneven, wrinkled effect.