Tony Alvarez pulled his SUV into the deserted parking lot before sunrise on a chilly January morning and unloaded two grocery bags, a jar and a backpack from his trunk as he waited for others to arrive.  It was 6:30 a.m. and he was expecting 15 people to join him for mushroom foraging in Tilden Park, an excursion people pay $100 to experience with Shroomy Walkabouts, a business  he started four years ago in the Bay Area. Participants arrived slowly,…