The masks at Universal Studios Japan come only in “Regular” size but have special Wizarding World-specific packaging!
The mask itself features crimson and gold stripes along with the lion icon and the word “GRYFFINDOR” in all caps across the front. These masks are quite thick, but may be too small for western visitors.
You can find these masks and show your House pride at Rodeo Drive Souvenirs, as well as merchandise carts across the park. At this time, masks for the other three Hogwarts Houses are not on sale at Universal Studios Japan.