In 30 plus years, I have never seen case lots of M2 Ball in Canada. 20 round boxes appear at gun shows from time to time, but not often. Won't be cheap.
"...where did you get the M2 casings to reload..." Any .30-06 case will be fine.
"...the correct ammo..." The rifle was designed and tested with .30 M1 ammo with its 174.5 grain, boat tail, bullet at 2647 fps MV, not .30 M2 ammo. This ammo was made for long range shooting but proved to have too much range for U.S. National Guard ranges. So ammo using a 152 grain, flat based, bullet at 2700 fps MV was developed. This eventually became .30 M2. In 1940, the muzzle velocity was raised to 2800 fps to match the ballistics of .30 AP ammo's 168 grain bullet.
The rifle functions and shoots just fine with any bullet between 150 and 180 grains. However, it prefers 165 grain hunting bullets and 168 or 175 grain match bullets with IMR4064, IMR4895 or Varget. And regular large rifle primers.
You must full length resize every time and watch the case lengths for any semi-auto.
Hornady's manual has an M1 specific chapter. Federal is loading a 150 grain FMJBT and a flat based 150 grain FMJ under their American Eagle brand for the M1 Rifle. They also load a 168 grain Sierra MatchKing under their Gold Medal brand. Don't know who has either though. Don't use any factory ammo in my rifle. My handloads only. Do not use any Hornady 'light magnums'.
This is good advice.....In addition, stick with powders that stay within the US milspec pressure curves for the issue 3006 ammo made for Garand use (which is why shooting "commercial" hunting ammo may not be a good idea..you don't know what type of powders are used in it) . Too fast of a powder "burn" (high pressure curve)will damage your rifle....too slow and it won't cycle/work. Also bulets heavier than 180 gr should be avioded as they can damage the gas system (not sure why, but I read this in an NRA publication on service rifle comopetition). Hope this helps.