If you're interested in acquiring an autographed copy of A Memory of Light, you can order them through Brandon Sanderson's online store.
There's an option to have it simply signed with an autograph only, or to have it personalized with a brief message.
Of course another option is to buy or bring a copy to one of the upcoming events that Brandon will be hosting. He begins his 3-week U.S. tour tonight in Provo, Utah.
Next month Brandon will attend JordanCon 6, along with fantasy author Patrick Rothfuss.