Tell us about yourself!
Office Depot, Staples, Walmart, Walgreens, CVS, BJ's, Costco, Target, K-mart, Ritz, or even at some gas stations that sell office supplies. It's called card stock.
Go to your office supplies store and just look for white card stock.
I have some duplicates that I'll gladly give you. You just have to pay for the shipping. My cards aren't even good. >.<