The other problem beyond the above mentioned is the right topography.
My land is 1 mile by 1 1/2 miles. On many parts of it I cant see 1000 yards. I do have plenty of spots where I can easily see almost the whole mile and a half prone. You will more than likely be buying a minimum 80 acre parcel. 1/4x 1/2 mile. I doubt you will find may parcels that are the size you mentioned because that is so narrow. Finding anything in the mountains you can shoot 1000 yards I bet is very difficult anymore. Now head towards Deer Trail and its doable. Grover, New Raymer, etc up north. Good look with your search, there is plenty of land that fits your needs out east and up north.