Lee will make a custom for you, I copied this from their website.
Collet Necksizing Die Set
A Custom Collet Die Set consists of the Collet sizer and the Dead Length Bullet Seater, a shell holder and dipper. Maximum outer diameter at the base is .555 and the maximum bullet diameter is .375. There are a few exceptions for the larger Ultra Mags and if interested in those, you may want to give us a call or send a case to determine whether or not we can make them. Order your custom collet necksizing die set here.
Payment of $60.25 ($55.00 + $5.25 processing fee)
2 fired cases from the rifle that the ammunition is to be reloaded for
2 sample bullets