There's no choice as far as what's being produced, you'd have to get one from existing inventory somewhere, the SB2 44mag is no longer made, but you can get an accessory barrel added to an SB2 frame.
I would caution you on getting an older rifle, I wouldn't get one older than 2007(HX or NX serial number prefix) and even then you may get a pre-Marlin made barrel, the accessory barrel is the best option to insure a tight bore.
Tim