While the "models" GK, MC and MCA were merely stock and finish varitions of the 1952 model, you will not find the designatin NO in any catalog. NOs were rifles or carbines custom made by the Steyr factory to the whims of individual customers. Most often they were one-off configuratins, though some were made in very small numbers. F.i. those special "Biathlon" NOs were made in two, slightly different configurations, both with GK-type straight buttstocks (that folding stock NO in the Steyr collection was a single prototype apparently): 18 such rifles were made for the then Biathlon team of the German Bundeswehr, about 20 for the team of the Austrian Bundesheer army.
As Rothhammer posted the 1960s Stoeger offerings, here are pages from contemporary German catalogs:
From the 1963 Eduard Kettner, Cologne, mail order catalog. The GK variation of the 1952 model only was offered, though a "monte carlo stock" is offered as an extra cost option.

From the 1969 Frankonia, Würzburg, mail order catalog (the German "Shooter's Bible"). The model 1952 GK is now shown with the tang safety. No mention of a Monte Carlo stock any more. Markedly fewer caliber options.

From the 1960s HAWEKA wholesaler caralog. Here the MC was offered as a sideline, but no mention of the MCA variant.