I am now in possession of 'rivnuts' and handles from a Chevy pickup.. we will see what happens next.. Thanks for the tip on the nuts, looks like they will work
You do not need to find any holes. Get the grab bar you want, mark the screw holes onto the mounting surface where you want to put it, pound in a nail or tapered tool that is a bit smaller than the screws to make a hole (don't drill-the nail will make a hole with a concave rim), and screw in some self tapping screws.