trying to re-sell trade Met tickets? need help

yes, Met tickets, I know they're pretty bad but this is my dilemma. I offered to donate four very good Met tickets to a charity. Through some confusion I ended up purchasing the tickets for a date that the winner cannot use (no fault of hers or mine- the charity mixed up some signals). 

 1. the winner expected tickets for a different night and cannot use the date I purchased

2. I really cannot ask the charity to buy the tickets I already purchased. I cannot attend that date, so  I need to unload them (NY Mets.com says they will not exchange or refund-but I will call them when they open this morning).  Ideally I would love if the Mets would let me do a straight exchange- I'm even willing to eat a few bucks even though my seats are for the better team (Braves (May 24)  and I would be asking for Cub tickets)...

3. I'll obviously try to sell the tickets I don't need on stubhub or somewhere like that, but does anyone know of a ticket swap or exchange that might facilitate this?