Buy a new handle from a Garden Centre or a good hardware store - it will come with an aluminium rivet.
Drill out the old rivet and remove the old wooden handle - trim the new handle to fit if necessary - drill a hole for the new rivet and use something as an anvil while you bash the rivet into a mushroom head shape.
Job done - 10 minutes.
If you're not confident ask an old codger to do it for you for the price of a pint.
An old codger
June 2010