This will be out with patch 2.4.2

It will be available from the Quel'Danas Gem vendor along with the following:

Quick Dawnstone: 8 Spell Haste Rating

Reckless Noble Topaz: 4 Spell Haste Rating / 5 Spell Damage

I do think these Spell Haste rating gems are a very good addition to Jewelcrafting.

But I have to ask... Where is the Melee Haste Rating love?