Hardly in sense 5 is used sometimes with not for emphasis <just another day at the office? Not hardly>. In sense 4b with a negative verb (as can't, wouldn't, didn't) it does not make a double negative but softens the negative. In “you can't hardly find a red one,” the sense is that you can find a red one, but only with difficulty; in “you can't find a red one,” the sense is that red ones are simply not available. Use of hardly with a negative verb is a speech form; it is most commonly heard in Southern and Midland speech areas. In other speech areas and in all discursive prose, hardly is normally used with a positive <you can hardly find a red one>.
Examples of HARDLY
It hardly matters what I think.
The changes in service have hardly been noticed.
There are hardly any new features in this software.
Hardly anyone showed up for the meeting.
Hardly a day goes by when I don't think about you.
This is hardly a new idea for a movie.
“Is this a new idea for a movie?”“Hardly! I've seen dozens of movies just like it.”