Performance Rights

Does anyone have any advice on seeking amateur performance rights for published plays. I do not seem to be having a great deal of success whilst trying to find out whether or not a couple of plays are available for amateur performance. In the first instance I have contacted Dominie Drama (who were very helpful), as they were not able to find out about a particular play I was after they suggested I contact the literay agent directly and provided me with an E-mail address to do so. I have E-mailed the literay a few times (over the course of a couple of months) and basically have had my queries ignored with no return correspondence what so ever. This has been the case with two separate literay agents including The Gersh Agency NY. I'm not sure if there are any other methods or options that anyone can suggest to help me find out whether or not performing a particular play is possible at this time.