The 45 Schofield is the same bullet as the 45 Colt in a shorter case. For a while in the late 1800s the U.S. Army issued both revolvers and that led to ammo boxes being stamped "45 Long Colt" to differentiate the ammo made for the SAA Colt from the shorter 45 rounds for the break-action Schofield revolvers. Eventually they simply issued only the Schofield ammo to make logistics easier as that ammo worked in both guns. It was a little less powerful than the full size Colt ammo.
I assume the 45 Schofield ammo is currently manufactured as guns are again being made in this caliber (may be popular with SASS shooters) but it will likely be harder to find at many stores than would be the 45 Colt and probably costs more. If you reload all that is not a problem. If you intend to shoot the 45 Schofield and you don't reload, you might consider starting.