I too have a new Model 1985 Marlin in 444 Marlin, and it is a nice big boomer.
As for current accessories, Budget Shooter Supply (
www.budgetshooter.ca) stocks .430 bullets in both lead and CamPro copper-coated, at decent prices. Look in the "Pistol Bullets" section.
For reloading, CamPro says their copper coating is thicker than Berry's bullets, and thick enough at .008" to make the bullet shoot like a jacketed bullet, so there's your powder load info.
As for older accessories, well, the Model 1985 is an old design, so there should be stuff around at gun shows.
Me, I'm putting a 3-9 x 40 Nikon scope on 'er, to do some more precision plus longer-range lobbing of shells.