Don't know what kind of Marlin it is, but I would probably cut the stock that's on it and buy a better one for the gun later.
But if that doesn't suit you, you might want to try to get a take-off through GunBroker.com or Auctionarms.com. These are consignment items that you can purchase out right or bid on.
Another source is Gunparts.com out of NY, but I find them to be a little high-priced for used items.