Anti-aircraft guns in the Spanish Army were considered Army Level Assets. They were neither mobile, nor were they attached to any organization smaller than a Corps.  They were used to guard airfields and other strategic targets.  At the onset of the Civil War there were just 4 batteries of 20mm and 2 batteries of 75mm AA guns in all of Spain.  The primary air defense was the anti-aircraft machine guns.*
*
While the Nationalists made more use of anti-aircraft guns than did the Republicans, they sttill used them primarily in defense of air fields.  The German 88mm was only rarely used against ground targets, being mostly used to protect the air and supply assets of the Kondor Legion.  The Italians made slightly more mobile use of anti-aircraft guns, but still primarily used them only for defensive purposes.  The primary anti-aircraft defense for all was the anti-aircraft machine gun.*
*
Anti-aircraft guns should usually be purchased in defend scenarios, and only in situations where air defense is normally a high priority.