This isn't to sound mean or anything, but you're actually wanting a solution to fixing a $3 flashlight?
I think 'buy a better flashlight' might be the first and most obvious solution. One that doesn't have a plastic pocket clip.
There are a number of mechanical pencils and such that have metal clips which attach to the pencil with a sort of ring, but the circumference would be too small to clip onto that penlight, I think.
If it doesn't sound too cheesy, maybe a paperclip rubber-banded to the penlight body?