Every biggish city has a distributor or three that sells to cabinet shops. They generally have laminates, cabinet hardware, paper-backed veneer and hardwood plywood. GP and Weyerhauser are just 2 of the names that have Walnut and oak for around $90, cherry and mahogany a bit more and even exotics. I bought 'Chinese Walnut' out of Columbus from DSI for $52 a sheeet which is quite nice.
Good quality hardwood plywood and iron-on veneer edge-banding make using solid wood a wste of time and resources, at least for large speakers.