First check your shocks shaft for corrosion. No corrosion, Mick Gardner Racing will rebuild for a very nominal sum.
If there is corrosion on the shaft then it's dead, Noleen J6 in the states have got the parts but it's not cheap with all the shipping.
If your frame is not size small then there are alternatives, Risse do a direct fit air shock, or someone on here has made an adaptor to fit a fox air shock.