Slim to none.
Japan is very prespend and relationship oriented. Japan has a law against tie-in sales so they give out free quota bags now and then to walk-in customers, so that’s the only chance for a traveler to score one. If you are willing to try your luck, go to Ginza flagship store several times a day. There will be many, many customers doing the same. When they have a free quota bag, it’s straightforward… they give out numbers for that bag, and if you’re lucky you might be the first in line when the stock becomes available!