Go on Sunday and stand out by the gate on the right side. starting about 2 hours before the leaders tee off. Have done this twice and gotten tickets with no problem as people are tired and ready to go home & watch it on TV. Two things probably go into this: 1] there are badges & not tickets so that makes it much harder during the week to just go for one day, and 2] the folks that have been there with badges all week are really tired, probably live close, and go home to watch all the key shots from many golfers from up close on TV.
My son & I along with Donald Ross went my first time the year Mickelson played with Couples in the final group. We needed 3 tickets obviously. We got right off the bat for $100 & let Little Reff go on in, got one about 30 minutes later for $200 & DR went in. Was starting to get worried but right before they teed off, I got one given to me and joined them at the first tee. We followed those guys all 18 holes & had a blast watching Philly Mick win.