Let It Snow

Let It Snow is related to the seasonal world event, the Feast of Winter Veil. Completing this achievement is a criterium for the meta achievement Merrymaker.

Locations
Handful of Snowflakes is a reward from performing  on a Winter Reveler, found in most inns. Other possible rewards are Fresh Holly and Mistletoe. The cool down for the kiss is one hour. As Handful of Snowflakes does not bind, it is possible to buy them off other players or the auction house, or transfer them from alts.

With the new expansion, Dalaran is no longer nearly as populated as it used to be, as it is no longer a travel hub nor the center of the world, thus increasing the difficulty in finding all the race/class combinations you need. Battlegrounds are a good source, and if you are willing to risk it, you can fly over your opposing faction's primary city (Orgrimmar or Stormwind) and hope to find and snowflake an appropriate character.