If you are not in a hurry, Arma 3 going to be available to buy on Tuesday and the highest package will include Arma 2:
http://www.arma3.com/buy
http://www.bistudio.com/english/home/news/projects/358-plans-for-arma-3-in-2013
*Edit*
Beaten by Tibbz2
Still, you can always get the the Arma II: Complete Collection (£25 on steam now) and the Arma 3 Digital Deluxe Edition for the same price as the Supporters Edition.
*Edit2*
BI studio link fixed
http://www.bistudio.com/english/home/news/projects/358-plans-for-arma-3-in-2013
Ideally just need a copy of Arma2 its for Dayz really for a friend. I can't see the standalone coming out properly for a while.