Making Type E Mag Tube Assy Inner 20 27/32"

I have an old Revelation 120 which is a store brand Marlin 99. I got it from a friend but I do not have the inner tube for the tube magazine. I have checked Brownells and I found a place that advertised them called Warner Guns and when I spoke to the guy there he said he makes each one individually for the firearm to ensure they fit properly. I am no gunsmith but I am pretty handy and I was just wondering has anyone tried this, or better yet know where I can find an old Type E Mag Tube Assy Inner