Likely a special order for factory .44 Special. All the major manufacturers load it. Remington, Federal, Winchester.
However, like t-star says, if you're planning on shooting it out of a .44 mag, it's better to load .44 mag cases to .44 Special velocities. Saves you having to clean cast bullet lube crud out of the cylinders too.
If you have a .44 Special firearm, just order it through your local shop. Likely be a 'money up front' thing and you might get a better deal if you order a case. Or you could just order 500 cases and load 'em yourself.