Get them on stubhub. There should be some good deals there as the Mets have been dumping tickets on stubhub for the last 2-3 years below face value. Get on the 7 train at queensboro plaza station and take the #7 express train 3 stops to Citifield. If you can't find anything on stubhub, there should be tickets available at the box office. Good luck. The express train has a diamond not a circle around the 7.