You can find the promos on the very own GeekMarket here on bgg!
The BGG Store image link is above "The Hotness" bar to the left on the website
Just to clarify: the BGG store and the GeekMarket are two different things.
The BGG store allows you to buy from BGG itself, and the M&M promos are sold out there.
The GeekMarket is sortof an eBay for BGG users, where you buy from other gamers.