You can find such magickal books in places like Thrift Stores-- I have actually seen Scot Cunningham's Complete Book of Witchcraft in several places, including Canada(My friend showed me a picture lol) Which is a blue-covered book with the pentacle on the front in like, light blue or something I think?
You can also find such books most likely online or Kindle. Kindle is recommended and also PDF if you have people who would otherwise scrutinize your choices and persecute you accordingly, etc.
You can find a lot of books on auction or biding websites, or even just on selling websites such as eBay, Amazon(personal favorite because they carry a pretty wide array, and don't seem to be so biased towards just christianity, unlike Barnes & Boring [Barnes & Noble] ), or any place online, really. Particularly, and of course, usually-- any book store.
I also recommend going into real stores in the flesh to truly get the sense of a book when you pick them out, as they will sort of jump out at you and are plain to see and judge, unlike their online counterparts which is hard to really get a good grasp of what they're about. But online may be cheaper, especially for Amazon.com, which can sell from new or used from a myriad of different vendors and warehouses and companies, etc.
Maybe even ask around to your local pagan, wiccan-- what ever-- group and community and see if they can lend you some books or materials if you're lucky enough in where you live.
Also search for metaphysical stores: they also may carry some books. Though becareful of the new age-y ones, they are usually just for the opportunity to make capital on all the young people wanting to search for something new and exciting. So be wary of the material at hand, and don't make decisions under pressure or time constraints, because more than not, YOU WILL regret your purchases.
I would suggest starting with the basics, such as what is Magick(and what it isn't!) and how it works, how to set up for your workings, how to meditate, etc etc and so on. You need a good foundation, like in any field of study, before you can move on. Otherwise you can literally end up sick or who knows, really, various things can happen given your level of knowledge and experience and etc.
Don't do anything if you have doubts, any at all! Blessed be!