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

Other days

gum

Gum Day
ride the wind

Ride The Wind Day
healing

Healing Day
youth

Youth Day
tulip

Tulip Day
ruby

Ruby Day
lumpy rug

Lumpy Rug Day
bounce

Bounce Day
blanket fort

Blanket Fort Day
pumpkin

Pumpkin Day