Has anyone had any luck getting extras with a massage at an all inclusive resort in Mexico or elsewhere?

Those jobs are so competitive, the locals aren't gonna do anything to mess it up.  Don't even ask, just enjoy the massage as its been better for me than spas in the U.S.

Prostitution is legal in most of these places. Do a bit of research on whatever city you are visiting and you can find all sorts of cheaper, better and more certain options, usually at a small fraction of what you are used to paying in the US.