Try Rainbow Grocery in the city. I know they have dried porcini and may have others.
For really fancy ones, Far West Fungi in the Ferry Building has different mixed mushrooms but they are expensive. I don't know if they sell a mix, so you might have to "create your own."
Also Italian delis like Lucca Ravioli in the Mission and Molinari in North Beach may have one or more different types of dried mushrooms -- definitely porcini.
Henry's, an offshoot of Wild Oats sells spices in bulk and they have dried mushrooms in bulk there. I've seen Whole Foods with many varieties of dried mushrooms however it is prepackaged into those to-go type containers and pre-weighed. You probably want to move this post to like a SF board or something though.