Bus: My May 15th pictures of the schedules at Manzanillo's main bus terminal show buses leaving for Zihuatenejo at 6:30 a.m. 6:30 p.m. & 10:30 p.m. Of course, schedules are subject to change.
Hiring a driver: You might try negotiating with a taxi driver after you get here. There are a couple of tour companies that advertise on the internet but I have no first hand experience with them. Not sure what sort of luck you will have trying to book this far in advance.
http://www.travelinvasion.com/FedericoLopez.html Email addresses only for the other 2:
chimaltour@prodigy.net.mxharotours@gmail.comIf none of that helps, we have a neighbour who does tours & who speaks English. Email me if you want his phone number.
laurie@mismosol.com