I find it is reasonably available. You'll never have the variety off the shelf as say .308, 30-06 or .223, but I find it just as often as less popular calibers like 7mm-08, etc. the run of the mill stuff tends to be $30-35ish a box on the low end, can go up to $50-60 a box on the high end.
For brands I have seen a bunch of different brands offering 6.5ammo, Winchester and Remington, PPU, PRVI, hornady, fiocchi, few others as well.
Locally you don't see it too often at places like Canadian tire or walmart, but any actual gun shop usually has some. Online most of the bigger shops offer it, but not always in stock. I have found that Tradex tends to have the best variety, but have found it lots of other places that carry it.
The only problem with most American made store bought stuff is that it is downloaded to fairly low pressures for the weaker actions of the krag rifles, so hand loading really brings out the best of the caliber, but you can certainly find decent factory stuff, just compare their listed velocities to either a reloading manual or a few other brands when you're looking at it.
(if I recall correctly, the downgraded stuff tends to run 2300-2500 fps, with the hotter loads in the 2800-3000 fps range, but that's from my not always reliable memory, so a grain of salt is required)