Yes, a GC method could be used for ammonia measurements. It would involve the use of a thermal conductivity detector which has a poor detection limit for this polar compound (around 0.1% v/v). A GC/MS (or perhaps a flame photometrec detector) would be much better.
Although few labs have a GC with a thermal conductance or flame photometric detector, many have a GC/MS. Good luck finding one that will take a production GC/MS offline to develop and process a few air samples.
But, ion chromatography is quite another story.* You will have to collect your sample on a solid sorbant tube (sulfuric acid-treated silica gel) or in an impinger. The impinger solution should be acidic (most often dilute sulfuric). Many labs do ammonia by IC. Google: laboratory ion chromatography. Look at Intertek.
*See NIOSH Method 6016. This is a clean air method. Modify it for your application. The impinger approach, although clumsy, may be the best solution.