Badger Ordnance does indeed make a single piece 20MOA taper for winchester actions, both long and short. I believe IOR does also, but will need to double check that.
Also, in a pinch, if you have a 1 piece base, you can shim the back side to get you some MOA. I generally do not like to shim bases, but with a 1-piece its not as much of a concern. But preference is to buy a 20MOA taper base.