Unfortunately you will have to purchase it. The physical book and roll20 digital merchandise are two different products from two different companies. Not only would you be paying for all the information that is contained in the product, you are also paying for all the labor used to format the material into roll20 digital layout so as a purchaser you can use it straight from the beginning if it is purchased on roll20. As you have the book in hand, you may always manually input the material yourself. Have a good game and keep the dice rolling.