clearbags.com has a lot of blank cards, envelopes, and plastic sleeves of all sizes. But they don't print. I hope you find someplace!
I am not sure if either specifically do cards. I get business and postcards from club fliers and really like them. A photographer at a show used whcc, and his work was very well printed. I have kept them in mind for printing on canvas, personally.
I really like Zazzle and I even signed up for a year of free 2-day shipping. I've printed cards on multiple occasions and have been quite happy.
The site is very user-friendly and you can get pretty good prices if you get quantities. Quantities can be mixed, too. One each of 100 designs if you like :) People can also purchase your cards from Zazzle at any markup you want but only if you want to post them. We've made a wee bit by just doing it with things we've made for ourselves.
ME&HE... loving our: dd(18) ~~ds(13) dd(13)~~ dd(10)