For my anti-air I get at the start of the match: 2 Chaparrel (vet3) [2 supply trucks along!], 2-4 Flakpanzers depending on the map. I also wield some autocannons (luchs, mbt70, etc.) and some infantry who can shoot air targets with their rifles. I leave 100-200 points in reserve!
After the game starts I recon as far as I can with a chopper to see my opponents unit composition and possible rushes beforehand.
IF I see a chopper rush:
1) stop your units to neares forest/cover
2) make sure your AA-units have a clear line of sight
3) call in either Rolands or any other AA-unit as many as you can.
4) create a flanking patrol of fast vehicles to go around the cloud of choppers to rush his base and end the game
-> haven't had problems with chopper rushes after the first week of playing