The simple solution here is the 88mm flak gun mounted on a half-track.  I forget what the designation was (you can google it), but they had them.  This game cries out for a real AA gun.  The 5" proximity AA rounds on the carrier groups are the only AA guns that really give anyone much trouble.  A ground vehicle version of the 88 would give us both artillery for pounding bases from long range, and a real AA threat vs bombers.