You should be able to find the plug your looking for at the electronic's store. You'll be looking for a 120vac(wall plug) tranformer to the 15vdc plug. On round (EIAJ type 12345)plugs the center is positive. There are many type's and size's of plugs, take the speaker with you. If you dont find a 15 volt output,,, 12 to 18 volts output should work too. Here are some links to ac/dc stuff.
http://www.anoma.com/linear-adaptors/output-plugs.htm
http://www.anoma.com/linear-adaptors/general-adaptors-namerica.htm
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