How can I fix my Valex lawn mower, TST 4638, 3.75 HP?

I need a metal part for my Valex lawn mower, TST 4638. The metal part in question surrounds the rotor and attaches onto the blade of the lawn mower. This part has a groove (or channel) in the side that probaby holds a thin retangular strip of metal, but this was lost in the grass when the part broke.