"Rimfire benchrest" might not be the best category for this question. I would look for a different site that specializes in old Winchester lever guns, or at least put the question in the "Factory/Hybrid Rifle" category of this site.
I checked gunpartscorp.com and they don't have any barrels in stock. You will likely have to have one fabricated from a blank and that is going to be pricey, if you can find a gunsmith to do it.