My suggestion is, depending on how many cards you need to print, print them yourself at home.
Red River paper have a lot of options for printing greeting cards.
Inkjet Photographic Papers Premium Photo Paper by Red River
Another source for doing greeting cards at home is a place called The Photographers Edge. The difference between this place and Red River paper is you print your picture on standard photo paper and then the card stock acts like a frame for the photo.
Photographer's Edge
I have used both but I do like Red River Papers printable card stock better.