What you describe sounds like a number 4, the largest farm bell made in Hillsboro. Because of the added weight it was not post-mounted with an upright but supported by a pair of A frames and usually placed on the roof of a barn, shed, summer kitchen etc. Spare bell parts aren’t abundant and restorers usually keep what they have for their own projects. A good machine shop can design the A frames, rope arm and clapper. The clapper ball should be about 3 1/2 inches dia and strike at the thickest part of the bell lip.