Where can you find a rifled slug barrel for a Winchester model 120 shotgun?

I see a Model 12, 121, and 1200 but no model 120, so first verify the model number.

For a barrel, try gunpartscorp.com, auctionarm.com, and gunbroker.com then start hitting the ads in Shotgun News. The model 120 was really a model 1300 slow budget model. It is the same inside the only difference is the wood on the 120 is plain hardwood. Where as the 1300's were offered with pressed checkering and also in synthetic versions. Here is a link to barrels that are made for the 1300's that will fit the model 120. http://www.midwestgunworks.com/merchant2/merchant.mvc?Screen=CTGY&Category_Code=winchester-model-1300-barrels