http://catalog.ammodepot.com/
Try these guys.....I bought a 401 die set from them...
If you need springs, I would try Wolf Springs, seems they have something that would work......
Cabella's have 351 and 401 ammo, expensive, but better than collector stuff out there to shoot.
The best thing to do, is get a set of dies, some 357 max brass, buy the bullets, and reload yourself, much cheaper.....
Old Lyman reloading books have both the 351 and 401 loads in them.
Hope your forend is good, there is a maker that makes them in California. I can look up the e-mail if you need it.
Great self-loaders, the 351 is equal to the 357 in power, and the 401, is equal to the 41 mag.....
A lot of Northern Woods hunters had them for years, and got rid of them when their ammo ran out, or the owner died. The 351 was a prison gun for a lot of years, til they retired them......