There are not many books on the subject. Most are already mentioned here.
IANTD has two nice freedive manuals. One for novices and another for more experienced freedivers. You could try to contact them about it.
There is Jacques Mayol’s Homo Delphinus, The Dolphin within man (ISBN: 1-928649-03-3) Beautiful book with lots of storeys and nice pictures but hardly any information on how to freedive or train for it but it might be interesting for a novice diver.
There is a very good German book: Dagmar Andres-Brümer's Apnoetauchen, Grundlagen Trainingstipps, Praxis (ISBN 3-89594-086-0)
There is a French book: Henri Corriol, La Plongée en apnée : Physiologie et médecine (ISBN : 2294009193)
Freediver magazine from Howard Jones is a nice magazine (
www.freediver.co.uk)
I am sure there are several other French and Italian magazines (if you understand the language). I do not know if there are English magazines on spearfishing, there might be but I do not know them.
Pippin productions used to sell instruction video's and other things on spearfishing/ freediving. I do not know if they still do.
I hope this helps.