Sears Craftsman makes a very similar SPL meter to the RadioShack analog one, and it probably is made by the same company that made them for RS.

http://www.sears.com/sr/javasr/product.do?BV_SessionID=@@@@1771511359.1073095863@@@@&BV_EngineID=ccjfadckflfidhfcehgcemgdffmdfko.0&vertical=TOOL&pid=03482297000&bidsite=&vertical=T OOL&vertical=TOOL&com.broadvision.session.new=Yes&com.broadvision.session.new=Yes