Where can I find Acuostic Research M-6 spkrs?


I have a decent mid-range system (Parasound amp/pre, old Thorens TT, Wharfedale Diamonds, AR M-6 and Monitor Audio B1 speakers in various rooms) and want to purchase a pre-owned pair of the AR 'holographic imaging' M series for a rec room in the basement. Does anyone know a source? Never anything here or ebay...thanks.
izmo