Valve has released the Treasure of the Fallen Cinder collection, which includes rare item sets for nine heroes, and mythical item sets for two heroes (click on the link for a preview of the set):
Phoenix’s Temple of the Fallen Sun set also applies a custom effect to the hero’s Supernova ultimate.
Fans can purchase individual Treasure of the Fallen Cinder packs for US$2.50. Each pack will contain one random set.
Alternatively, you can look out for specific sets on the marketplace. Right now, Phoenix’s set is going for about US$10, while the Wraith King set is a hefty US$30.