Yes, I have the book. Frankly, unless you want the book 'to complete the set', I wouldn't bother to seek it out. It contains very little that is specific to the Cowells machine, except a screw-cutting chart and parts diagrams. If you're new to lathes, you won't learn enough from this book: if you're not a newbie, you don't need it.
The owner of Cowells is/was very approachable and helpful. If you need any specific info., I'd expect you would get a good response from him. You might also get a copy of the book from him. And, of course, there's a mine of info. available right here, on this forum – just ask.