The present invention discloses methods to produce large quantities of polycrystalline GaN for use in the ammonothermal growth of group III-nitride material. High production rates of GaN can be produced in a hydride vapor phase growth system. One drawback to enhanced polycrystalline growth is the increased incorporation of impurities, such as oxygen. A new reactor design using non-oxide material that reduces impurity concentrations is disclosed. Purification of remaining source material after an ammonothermal growth is also disclosed. The methods described produce sufficient quantities of polycrystalline GaN source material for the ammonothermal growth of group III-nitride material.