The simplest way is by giving them a cold-call and an email.
However, you can also contact a station through the PRX messaging system:
From a station's PRX profile (which you can find by searching for the station's call letters or name), click "Contact [station call letters]" on the right.
Make it easy for a station to understand why you are contacting them about a piece. For example, if there's a music festival going on in their town, and you interviewed one of the bands in that festival, be sure to briefly explain the connection.
Sorry, but we don't allow mass-messaging of all the PRX stations. With as many members and pieces we have, you can see how that might get out of hand.