There are basically two sets:-
Trevor Thom series or Jeremy Pratt series.
This has been asked many times before (usually in the Private Flying forum). Please do a search on "PPL ground school/study" whatever and chapter and verse will be laid before you. As for where you can get them, there are numerous flight suppliers on the internet - eg Transair, Pooleys, Flightstore, AFE,.. you usually get their catalogues free with one or other aviation magazine. Costs £20-£25 per book?
Cheers
Whirlygig
PS - I am assuming you mean UK here as well.