Would you not be able to use normal .458 Win Mag dies? Even .45/70 dies would work. Just have to adjust them accordingly.
I use a .458 Mag. seating die for my .45/70 - works just fine. I simply shortened it so I could crimp the jacketed bullets due to the .45/70 being 4/10" shorter.
The Lott is simply 3/10" longer than a .458 Mag. So, adjust the die so there is 3/10" or a tich more between the shell holder and the bottom of the die & done deal.
If using brass that's been fired in your rifle, or new brass, there will be zero problems with this, even when crimping on seating. Stronger bullet "pull" is good when using straight cases.
'Course, if you want Lott dies, then have at it. It's just that they aren't necessary, when more easily obtained dies are also likely less expensive.