Mag isn't going to be easy to find. Model 16 was only made for three years (1990-1992). Even the Model 16 K-32 Masterpiece is rather scarce, only bout 3,600 made from 47-74. The Masterpiece is chambered for .32 S&W Long only and the later Model 16 would take either the Long or the Mag. Book shows 335 for a 100 percenter maggie but gonna be tough to find a cherry one that the owner would part with for that price..
Watch Gun List, Shotgun News.....and post your wants on all the boards you can find.
I wish you luck in your search. Personaly I would rather have the masterpiece but they run well over a grand for a nice one.
Sam.....me luvs them older Smiths.