+1 on start with G+L.
Failing which, England is full of remarkable specialist outlets selling every imaginable nut, bolt, screw and fastening.
So long as you can accurately measure the part(s) that you want to replace, you'll find someone operating out of an obscure industrial estate in the Fens.
If all else fails, I have just such an outlet 50 yards from my studio in West London (on an industrial estate, natch).