There are many out there. Have you looked up any rose nurseries online? The clickable link at the bottom of my post is a thread which mentions quite a few. If you visit their websites, look for Moss roses there. Or, if you know the names of particular Mosses you want, look them up on HelpMeFind, then click on the Buy From tab to see where they're being sold.

http://www.helpmefind.com/rose/plants.php

:-)

~Christopher

Here is a link that might be useful: List the reputable remaining rose nurseries