If you're low on continues, and need desperate help 
for gems, you're in luck. Go to the Blue Resort 
level, then play stage 1, switches and bridges. Play
through until you come to a large brick building with
a ton of windows. Search for an open window and toss 
a pumped bomb inside the window, stand back, and after
it blows up, enemies jump out. They die right after 
they land. Both blue and red gems come flying out of 
the ruined building. Sometime later in the same stage
you'll come to another building like the first. Repeat
the process and you can get more red and blue gems.