If you have all the pieces, it's usually pretty easy to use Acra-Glas to reassemble. Can be done so the repair is almost invisible. Missing bits can be patched with similar color wood cut from scrap blocks. Weak areas can be reinforced with threaded brass rod. I've replaced heels, toes and pistol grips that way. Could hardly see the joints when refinished. Brownell's has what you need to do it, including dye for the Acra-Glas.
At one time Gun Parts/Numrich had spare Marlin-made levergun stocks, you might check. Otherwise it's the aftermarket for you. Brownell's had some at one time, check their website for current availability.