From what I've observed, most people who have a lot of extras, come in with several terrace seats. You'll see people leave with a bag full of bobbles. I went with a friend to a bobble day two seasons ago where he had purchased some 10 seat deal in the terrace, that came with vouchers for hot dogs and sodas. He got 8 bobbles that day. Also, after the game there are at least two people I always see, standing outside offering people $5-$10 for their bobbles and they seem to get a lot of takers.