At US Open tennis tournament can you buy a Grounds Day p from a spectator who is leaving?

I've heard that in past years you could do this-- i.e. you don't have to be the same person who used the p originally. As long as you're more than 1500 feet from the venue, you're not breaking NY state law. Can you do it this year? And if so, what's the best time to show up and what price can you expect to pay? (presumably well under face value). Where's the best place to stand? Any other helpful hints? Thanks.