And it's ridiculous to pay scalpers over $100 for a grounds pass that costs $46.
Granted, I have never been to the USO but I have gotten tics for numerous sporting events/concerts that have been sold out and maybe some could be applicable.
If the scalpers are having trouble selling, they may lower the price if the USO is anything like other sporting events that I have attended. (And for various sporting events, I have bought 3X the price of tickets down to below face value from scalpers.) But sometimes, if it is something you really want to see, it can be worth paying much over marketprice and then scrimping a little later.
You may also be able to try a ticket broker. Granted, you will have to pay over market value, but sometimes they can be not as outrageous as some scalpers.
Do they sell grounds passes on Ebay? (I know they have AA and LA tics for the USO and I got all of my tickets for the 2003 and 2004 TMC finals off of ebay.) Also- does the New York area have craigslist? You could check there.