I think that the Mach IV is a wildcat from the 1950's that was used for match shooting. I don't know of any commercial ammo or rifles that were ever made. If you want 17 centerfire go with the 17 Remington.
17 Mach IV ammo is commercially made by Cooper Ammunition. The point is mute now as I have decided on a .221 Fireball using 37 grain hollow points. Thanks for the response.