They're in Sawtelle Japantown Caps. As you may have heard, Sawtelle Japantown is the new name of the neighborhood that encapsulates the GR stores. The history runs deep and the name will outlive all of us. The caps are available at Giant Robot Store on Sawtelle and online here.
I wrote about Sawtelle Japantown and the name change when it happened at Yomyomf blog.