I got totally confused when I read the title of this post. My 1300 defender came with a sythetic stock and later, I added a pistol grip. Would it help if I said you needed to buy a new shotgun ??? That is when you really won't have to. I've see complete used stock set for these, for about $35.00. Wood or sythetic, are readily available. .....
My Defender bought in 1984 has never had a part fail or a fail to fire or extraction. The 90's 1300 you have is 3 times the shotgun of a Steven's. The Steven's is a 5 shot and the 1300 is an 8 shot and I doubt there are mag extensions for a Stevens. More accessories for the Defender as well. Not to mention the Winchester has the smoothest action of any pump shotgun. Put a Hogue short or Knoxx recoil stock on it and enjoy it for many years.