So I do play BF3 (on PS3) a lot, I've racked up about 60 hours gameplay but every time I look at my vehicle stats I can see I have absolutely no points for the AA! I can't believe I've been playing so long and haven't even apparently been in this vehicle. So was just wondering where on earth I can find this Anti-Air?
Assuming you are on PS3 based on your Battle-Log the only two maps with mobile AA to my knowledge are:
The small number of maps with available mobile AA is probably why you haven't seen it yet. It spawns far back in the base at each set of points in Noshaar and it spawns I believe at the airfield in the hangar on Wake Island Conquest.
They are mainly on the large conquest maps that have air vehicles, and are very hard to get because people hoard them and hide in places with them. It all depends on what map you are on but they will only spawn at your main base not any of the checkpoints.
But generally if the map has flying vehicles it will also have AA's.