there are a lot of places that sell both. http://rareseeds.com/vegetablesa-c/carrots.html Baker's Creek has both and they are heirlooms and non-GMO stuff. http://www.johnnyseeds.com/c-18-carrots.aspx is another good place for lots of different carrots in different colors. if you are looking for the 'Black Knight' carrots they are found under the flower section with the false queen Anne's lace. i have been searching for the 'dragon' carrots but they seem hard to find being sold with all the other colored carrots i want to try.
I know this reply is a little late but I just ordered red, purple and a mix of white, yellow and orange carrot seeds from Park seeds. http://parkseed.com/