Oops, it doesn't look like 'mourning following day' is a national day..

Other days

buddy

Buddy Day
carpenters

Carpenters Day
tell a fairytale

Tell A Fairytale Day
ruby

Ruby Day
law

Law Day
gum

Gum Day
ponytail

Ponytail Day
brow

Brow Day
kiss a ginger

Kiss A Ginger Day
kale

Kale Day