Thermodynamic functions and pair correlation functions obtained from numerical solutions of the hypernetted chain (HNC) integral equations are presented for two lattice gas models in which the interaction energies are chosen as far as possible appropriately for cation vacancies and divalent cation impurities in AgCl. For the primitive model, where the interaction energies are coulombic at all separations, results have been obtained to very high defect concentrations. For this model the configurational energy, defect activity coefficient, and lattice gas compressibility are qualitatively very similar to those predicted by the analytic method of Walker and Gillan, and both thermodynamic functions and pair correlation functions are qualitatively similar in character to those of the restricted primitive model of electrolyte solutions. The results for a modified model, which incorporates more realistic estimates of the defect interaction energies at first- to third-neighbour separations, differ substantially from those for the primitive model. Results for both models suggest the existence of a spinodal boundary which it was not possible to locate in detail. The solid solutions also become metastable with respect to ordered Suzuki phase structures at high concentrations.