Two main ones. Battlers connection and model ships ahoy( who posts much of his Hull offering in the for sale forum)
Neither of those sells a Montana Hull. Strike used to, but they don't sell hulls anymore. Other manufacturers (less major) to consider are Bowning Ship Yard and Dreadnought hulls. Montana is difficult for big gun but rewarding and not legal for fast gun so not may people produce them.
I probably won't do Montana right now, I was thinking of a Des Moines for fast gun and maybe a Benham for big gun if I can get my hands on a hull. If not a Benham(not Fletcher kind) maybe a Clemson
I did want to put rotating turrets on the des moines but apparently it doesn't fit the requirements for fast gun so I might do an Iowa
I think you can get plans from the Smithsonian but I don't think that there are any hulls to be found
1106 skyway drive. Annapolis. Starting by 10. Look for red truck in the parking area. There is a door on the side of the garage next to the camper, we’ll be in there
Bring a camera and a note pad. Make sure you have extra cash for parts and hulls. Plan on most of the day there.