Just go to the crown tail section and look through them, dragons will usually have dragon in their titles.
I don't see any dragon scale CT's for sale, but you can get dragon scale HM's and breed them to your CT's.
two breeders with a few to choose from are smilebetta:
They have an email for fish girl in the shipping info, you have to contact her before you order fish because she will be the one who get's your fish from the thailand shippers and send it to your house. ^^
If you wanna wait and keep looking, at the top of the page is a searching thing. in the scroll menu find crowntails, then type in dragon and search. ^^