Mine cost a little extra because I had George wire it with 2 volume controls. He referred me to Allied Electronics for a Stancor regulated (very important) power supply. Mine is also wired with the center pin negative on the PS since that is the way the Stancor is wired. I've always been curious as to the battery PS, but this time I think I'll leave well enough alone.
http://www.alliedelec.com/search/productdetail.aspx?SKU=9289895
http://www.alliedelec.com/search/productdetail.aspx?SKU=9289895