I wrote GE asking this very question last spring, after downloading the book in its entirety. The answer they gave me was basically what other posters here have already suggeseted - since the book was published so long ago, no one at GE has any record of the solutions manual. It is not available online, in print, or in any electronic form.
However, while this book has stood the test of time, it is still quite antiquated, predating the microprocessor relay by a good 20 years. "Protective Relaying" is a more modern text by J. Lewis Blackburn, also with problems at the end of each chapter. I have not researched the availability of the solutions, but I would imagine they are much easier to come by than the GE book.