Some years back I found some aluminum tubing at work that rectangular in cross section but had rounded corners on the outside (inside had square corners). I used this for the lower "handle" section. I then hunted down a piece that was close for the inside sleeve.It took some file work and sanding to get a fit but I did.
Actually I have made one with only an outside sleeve and used no sleeve on the inside. Just fitted the upper limb real close to the inside dimensions and bedded it in with JB Weld. You want to use a heavy coat of paste wax or such on the inside of the sleeve to work as a release agent though. Otherwise you end up with a one piece.