Why is it that I can't find LRN .401 projectiles?  Do they not exist??

There have been some usually made for the 38-40's, the ones for 10mm/40cal are usually FLAT nosed or TC configuration.
That keeps them shorter in overall length leaving more room for powder. 

Ahh, yes, ok. 

At a quick google search I came up with these that catalog a 155 grain RN WC

http://www.meisterbullets.com/AWSCategories/p/22/Hard_Cast_Bullets_
http://www.thebulletworks.net/Lead-Cast-Bullets-s/1.htm