That barrel was a limited run and I got it from Green Mountain. I heard that a bunch of long range shooters were begging them to make a 1" barrel that was 32" long, and 1-18 twist. I have used 475 gr Lyman whitworth bullets in it and they shot good. Now I use the Lee 459-405-HB for that gun and I paper patch them and size them to fit the barrel. I went with a little smaller bullet because this rifle was built for an antelope rifle.
I don't know how many they made but they are sold out, you might keep your eyes open and find one. I know there was one pop up on Monster Mulies for sale about a year ago. Green Mountain does have some 1-28 twist Stainless Steel 45's but the bore is more in the .451 range, I got mine for 110 dollars. Ron