Happy Mask Shop

Ocarina of Time
The Happy Mask Shop appears in Ocarina of Time and is located in Castle Town. It is the basis for the Mask Trading Sidequest, and will only be available after the guard in Kakariko Village receives Zelda's Letter. You can only get the next mask after you sell the first mask. The masks not for sale are all useable by Link after you sell the Keaton Mask, Skull Mask, Spooky Mask, and the Bunny Hood.

Masks for Sale
 * Keaton Mask
 * Skull Mask
 * Spooky Mask
 * Bunny Hood

Masks Not for Sale
 * Mask of Truth
 * Gerudo Mask
 * Goron Mask
 * Zora Mask

Oracle of Ages
A smaller version of the Happy Mask Shop, can be located in Lynna Town in Oracle of Ages. However, masks are unable to be purchased at this particular location.