From what I gather the Cheytac is pretty much unobtainable. There is, however, another company who makes basically the same rifle. In fact, IIRC, they used to be partnered in the M200's development and had disagreements with Cheytac and split. The company is EDM and they call their version the Windrunner.
It is offered in multiple chamberings but I believe the one you're interested in is .408 Cheytac. .408 CT with a 300gr bullet will leave the muzzle in the neighborhood of 3500fps.
Neither the rifle or the ammo are cheap or easy to come across, expect to pay well over $5k for the rifle and over $4/round for ammo
Sgt. of Marines, 5th Award Expert Rifle, 237/250
1st Award Expert Pistol, 382/400
D Co, 4th CEB, Engineers UP!! OEF 21JUN-20SEP2011