[Paul B.]

The Lyman 310 tool AKA The Nutcracker" doesn't use shellholders. They use special dies that neck size only. Midway may sell some, but in checking the Lyman site, they have very few die sets that they make any more. They have discontinued most caliber sets.
Earlier dies sets had five dies, one that decapped the fired case, one that sized the neck only, a primer seater, a neck expander and finally the bullet seater.
In a cost cutting move, they combined the neck sizing and decapping die into one doing both jobs. Frankly, I don't much care for the four dies sets. While Lyman says it is a time saving convenience, I find that die to be a bit stiffer to work.
It might help to know which cartridges you are wanting to reload with the 310 tool as to the availability of dies. I have quite a few and I do use them, even though they are slow to work with. Amminition loaded with those die sets can be exremely accurate.
There was a fellow that collected and sold 310 tools, but his site closed down over a year ago. Probably your best bet would be to look through the gun shows. Anytime I see a set for any cartridge, or even partial sets I buy them. Wish I could be of more help.
Paul B.