I really love paperandmore.com.... I got a lot of their metallic papers from them when I was traditionally scrapping.... they also have regular cards, too... but I never tried them. If they are anything like the quality of the metallic, you won't be disappointed.
Not sure if this is exactly what you are asking, but I have bought cards at hobby lobby or michaels before. They are prefolded and come in several different colors and sizes. Then, you can add whatever you want!