The Script Co. has a large catalog of available plays for theater production, they are not interested in movie and TV scripts and their catalog does not contain any plays with adult content. The catalog is made up of plays from writers around the world. Theaters of various sizes and in various locations pay the Script Co. for the rights to put on the play. The rights they offers these theater companies are temporary, and after the play the scripts are returned to the Script Co.
Their website, while informative, does not give information about the royalties scale. However you can requests the details directly here: http://www.thescriptco.com/write-us/. Just write them and ask to learn more about the royalties they pay authors. I have seen the details. I can tell you that the writer receives 30% of the lump sum the Script Co. receives from the theater. That means that if the Script Co. receives $165 from a small production of the play, the writer will receive 49.50. All the costs associated with printing the play, shipping it, and various other costs are covered by the Script Co. Royalties are paid quarterly.
The Script Co. - Submit My Script
http://www.thescriptco.com/submit-script/[/size]