It was hard to know where to start: He only knew one artist, his school art teacher. He found others by searching illustrators and artists on the Web, contacting artist associations, through referrals from Reach Out and Read, and by shooting for the stars. He wrote, for example, to glass artist Dale Chihuly, whose work he’d seen at the Museum of Fine Arts. (“If he wanted to do a glass tree, Isy was all there for it,’’ said his mother, Becky Behar.) He wrote to Michelle Obama. She isn’t an artist, but she’s big on children’s literacy, Isy explained.