This
>>13502732 is what I did, though I took maybe 3-4 encounters before that to bring it down to red HP and put it to sleep. If it wakes up and runs I just soft reset and try again. Saved me tons of money on Premier Balls that way too.
It's probably going to take you several encounters if you use a freshly caught Wobbuffet, as any attacks will nearly/OHKO it. The best way I found to keep running into them is to run back and forth between Routes 34, 35 and 36 while checking your map.
This is what I did to get them right after they ran out of the tower. If you're further along in the game or have more patience for preparation you might try a method like this
>>13502741 
