It would be cool if PG came out with this type of stones in order to build or finish up certain dragons!!
Welcome to the froums! We have all made mistakes in the game or made decisions we later regret. However, as posted in November, limited-time items/dragons are meant to be limited time.
Next time, please make use of the “search” feature on the top right hand corner of the page to see if your question/suggestion has already been answered or addressed!