You're right on about those old Pocket Rocket Magnum tubes Ed. They were some of the most powerful tubes I ever shot. They were a perfect match for 7/16" lead or 1/2" steel balls. They have been out of business for years now. You could try McMaster-Carr. They have EVERYTHING. Maybe some of the tube guys will chime in here and give you some advice.You can always load flats on her.