i am only finding some but minimun qty are 100, 500, 1,000 or more.

maybe try walmart as kfamr did, or you can ask to a copy place, you can get a cd with the file and have it printed on a paper you want and in color, i´m not sure if you do that in the states but i do it frequently here, you get a nice resolution and its not that expensive.

edit: i just found this sites dont know if it works for you
http://www.postcardbuilder.com/?request=misc.pricing

http://www.48hourprint.com/