Yes, but they are not cheap- $135. Numrich Gun Parts Corp. - The World's Largest Supplier of Firearms Parts and Accessories
Ref: magazine- in all likelihood, no. Federal game law in the US limit shotguns to a max of 3 rds when hunting migrant birds, so most makers limit maga, except tubular mags that can take a plug.
And not to be cute, but if you have been searching under marling, computers are very literal minded little critters, they will not look for a marlin if you said marling.