Guest,
The Model 1910 was first introduced in 1910 and produced until 1936. The highest serial number listed is 20787. So they are not real popular. As a result major ammunition makers do not produced this .401 caliber any longer. I did not find it listed in a couple of other specialty ammo manufacturers. It may be that you will have to find some custom brass and reload them yourself. You are realy going to have to want to shoot it.
You might follow this link to another forum. Sounds helpful.
http://shootersforum.com/showthread.htm?p=208254
Then you might start hitting the gun shows and doing some digging around. If I hear anything else I'll pass it on.
2bit