According to the preface, is it only possible to find a Sadguru in a specific form, like a holy person?

No, a Sadguru can manifest in many forms. The preface, as detailed in Chapter 0, explains that a Sadguru is not limited by caste, religion, or age. They can be in person or even in the form of a book. The text further clarifies that a Sadguru can be a saint, a deity, or even one's own mother, father, siblings, friend, husband, or wife, whether they are known to you or not. This highlights the broad and accessible nature of a Guru's presence in one's life.