Hey Dave,
Sucks to hear about your problems with Navionics. Their coastal water charts in those regions are definitely not as good as their inland water charts but maybe it's possible that you are missing updates?
Anyways, I know that you can purchase charts from other chart manufacturers on iNavX. I own a set of CHS charts (the Canadian version of NOAA) on iNavX BUT, Navionics is the only manufacturer that have charts available of the Panama region on iNavX...