Bron Yr Aur Stomp is a stranded colorwork hat design made to work with 4 colors of O-Wool Sport mini-skeins.
You can find yarn kits from O-Wool here.

The main sample used O-Wool Sport mini-skeins in 4 colors:
MC: Salamander (58 yards)
CC1: Bee Balm (45 yards)
CC2: Sun Fish (32 yards)
CC3: Devil’s Pool (58 yards)