Alaska Airlines is not part of any global airline alliance, but has ties with many airlines for earning and redeeming miles.
Alaska Airlines has launched (yet another) Mileage Plan miles sale at up to 40% bonus that is valid until June 13, 2016.
You can access Alaska’s web page for buying and gifting miles here.
Note that Alaska Airlines doesn’t limit the number of miles that you can purchase over calendar year. They merely have 60,000 miles limit before bonus per transaction (used to be 40K).
The price of an Alaska Airlines miles purchased at the max bonus level is 2.11 cents each.
You have to bear in mind that Alaska may change their award charts overnight without any prior notification to its programs member just like they recently did with Emirates awards (read more here and here).
It still can, however, may make sense to purchase them if you can find reasonable use with partners such as Cathay Pacific.