I don't know if you'd want to use an iron-on, but there are lots of places that do that type of service.
Here's some of them that were posted previously that you can contact to see if they can do what you need:
http://www.t-shirtforums.com/showthread.php?t=4095&highlight=custom+plastisol+transfers
Here's some of them that were posted previously that you can contact to see if they can do what you need:
http://www.t-shirtforums.com/showthread.php?t=4095&highlight=custom+plastisol+transfers