The Elite bus has been running up and down the coast between TJ and Acapulco as long as I have been living here and probably much longer than that. It does stop in PV and in Manzanillo and also in Melaque - though neither Manzanillo or Melaque is listed as a selection in their on-line schedule. There was a store on the street in Melaque that the bank is on - heading towards the principal street (the one the Jardin is on) from the bus station that sold Elite tickets in the past. I've no idea if they still do. The folks at the bus station should be able to tell you who does or since someone Sparks knows bought a ticket I would imagine that he also knows where they are sold.
Elite line is owned by Estrella Blanca and their route map and schedule can be found at
http://www.estrellablanca.com.mx/main/index.htm when you pull the page up select Primera from the top tab menu and Elite from the pull down menu within that.