I am looking for the story about Gajanan Maharaj's interaction with a wealthy Parsi merchant who wanted a son. Is it in this book?

Based on the provided excerpts, this book does not contain the story of Gajanan Maharaj and a Parsi merchant. Instead, Chapter 14 narrates the story of a different spiritual figure. It describes a famous, wealthy Parsi merchant named Ratanji who was distressed because he had twelve daughters but no son. Following the advice of Das Ganu, he traveled to Shirdi to seek blessings. The narrative clarifies that the holy person he met was Sai Baba. Ratanji went to the Masjid, offered a flower garland and fruits to Baba, and prayed for help. There is no information in these specific chunks to suggest any connection to Gajanan Maharaj.