Discos de Ayer, Bop!, and ABC Discos before coming here.
Revolution Records also seems to be the place where old music guys just come and hang out. I never see anyone buy anything here, but there are always several guys just hanging out, talking about music and other things.
Revolution Records is located at Insurgentes 395 in Condesa, right on the corner of Insurgentes and Campeche. The google maps link is off by a block, but it will get you there. The store is right in front of the Metrobus stop Campeche, or you can get off at Metro Chilpancingo and walk north on Insurgentes a few blocks.