Upgrade your house to max, keep your hunters in town at least 1 lower than the cap. This will make random hunter come to your town every 10 minutes instead of 60 minutes.
If your town was full, you need to wait for 60 minutes, after that it would all be 10m
If your town was 15 out of 16. By using this method you will get more book every 10 minutes.
How much you gonna get for each tier hunter:
Normal : 2 Books
Rare : 4 Books
Superior : 8 Books
Heroic : 16 Books
Legendary : 32 Books
Colosseum also drop books when you win, but it is random, and it give only 1 book.
To get a secret tech up to 100, you will need 375 books.