I doubt you're going to have much success this late on a message board. My suggestion is you go out to the game a couple hours early and walk the parking lots looking for no-shows, people getting sick or with last-minute conflicts.
Get your kid to make up a humorous sign and walk around with it. You're more inclined to find someone wanting to reward a kid in that situation. And it will tickle the seller when your kid goes bonkers!
Good luck...