Mk. II** rifles can be issue or private purchase. If issue, there will be stampings on the buttstock. Private purchase rifles were intended for service rifle target shooting, under the auspices of the Dominion of
Canada Rifle Association. Same idea as NM Springfield rifles.
Mk. II** rifles were intended for range use. These were the .303 rifles that swept Bisley, resulting in complaints that they were not actually "service" rifles.
There are variations in rear sights, and in the end of the forend, with different lengths, nosecaps and bayonet mounting provisions.
Mine is a fairly late one. It has a BSA Martin finely adjustable rear aperture sight, never had a barrel mounted sight. The bedding surfaces still show the carbon/soot from the hand fitting that was done when the rifle was set up in the Ross custom shop.
Mk. III rifles, apart from the Home Guard ones, are service rifles. Their rear sights are basic, compared with something like the BSA Martin.
As far as availability goes, think in terms of finding a low number Springfield rifle with a crisp bore, or an early NM springfield - only with much smaller production numbers.
If you look around this site, you will find photos of a Mk. III HG, a Mk II**, and a Mk. III sniper rifle.