Cold-weather flying

Hey guys
With the gold squish incomming I thought I would invest some of my gold on Cold-weather flying.
Im a level 72 druid playing on the alliance side, and I've seen toons lower level than I flying around in Northrend. However I can't buy it in Dalaran and the riding trainer in Valiance Keep can't sell it to me either.

Can anyone help me?

Cheers

you need to be level 77 to buy the book, you can however buy it on 1 character and mail it to another.