I print them myself as well. A friend of mine also does reasonably large quantities himself as well.
Lots of the on-line print houses do them now as well. Printroom is one that I tried long ago and they messed the orders up, but more importantly to me, they were just too ordinary looking for my taste. Small orders were no problem.
Lisa mentioned Crane's Museo card stock; Red River Paper also sells several paper types and sizes pre-scored for folding, and Hahnemuhle has an offering as well.
If you do decide to print them yourself, be aware that some printers struggle with the feeding of note card stock, so you may want to look into that. In fact, whether or not you use Red River products, they do have useful info on their site or you can talk with them about some of the feeding issues, etc.
Sorry, not really an answer to your question.
