You PROBABLY could also buy that from Marlin if you can't find it anywhere else.
Staying at 32MM or smaller for the scope is good, too, (if you must use a scope) in order to get the lower mounting height. Shooting budd put a 4-12x50 on his Marlin336 and had to use some super-tall 'see-through" mounts. even with that, the front lens just barely cleared the rifle. Looked kinda silly...
I have a 4x32 on my Marlin Mdl 30AW, so mine is not a "traditional" sighted rifle either..but that 4-12x50 looks well silly. Wisjh i had a pic to show you, but I don't.