The “no unsolicited submissions” policy is in place to save the studios, producers and agencies from any chance of plagiarism accusations. To make an unsolicited submission solicited send a query letter to the agency that tells them you are looking for representation and that describes your work in very general terms without revealing any plot or character details. Nowadays agencies sometimes accept query letters by email but most of them are still expecting a regular letter of the most ordinary variety with a self addressed postcard or envelope enclosed. There are companies like Jerrol LeBaron’s InkTip, trying to solve this problem in some other ways.