I dont think there are any helicopter magazines you can get in a newsagent and for me the main ones I read are these three:
1. Rotor & Wing - which is free and you can subscribe here
http://www.omeda.com/rw/
2. Heli-Ops - great articles and photos which you can subscibe to from here and they are from New Zealand I think.
http://www.heli-ops.com/
3. Vertical - another good magazine with superba articles and photos from Canada.
http://www.verticalmag.com
Now and again you will find a few helicopter articles in Flight International and some of the pilot magazines which you can getin your newsagent.
Also PHPA(Professional Helicopter Pilots Association) give you a subscription to Autorotate when you join them -
http://www.autorotate.org/autorotate/
And of course HAI(Helicopter Assocation International) give you a subscription to Rotor when you join them - a very resourceful magazine -
http://www.rotor.com/
Let me know if you know of any others.