We met him easily on Buena Vista Street at DCA in December with just one other party in front of us in line! He was sort of off in an alley near the gas station on the left just as you enter.
Yes, when you walk into DCA, there is a "bridge" that crosses over Buena Vista Street. It used to look like the Golden Gate bridge before the re-imaging of DCA. It's actually the monorail track.
Right when you walk into CaliAd, he's there. It seems like there's an Oswald's Auto Repair or something like that just to the left when you first come in. I guess that's why he's there.
The bridge is right as you walk into the park, can't really miss it. I haven't seen Oswald, but he should be near the store with his name, which is just before the bridge.
NM-I'm too slow.
Oswald started out in the covered area between CoC and F&D, but he now hangs out immediately to the right of the gate, before you get to the lockers, or sometimes in the center seating area between Oswald's and the lockers.