“Distributor” means any person that engages in the operation of selling, marketing, or distributing, in intrastate commerce any commodity which he has produced or purchased or acquired from a producer or which he is marketing on behalf of a producer, whether as owner, agent, employee, broker, or otherwise. It does not, however, include a retailer, except a retailer that purchases or acquires from, or handles on behalf of any producer, any commodity which was not previously subjected to regulation by the marketing order which covers such commodity.