There should be. Compulsory four is very important and there will be no shortage. Because compulsory three is algorithm, some schools may choose to talk about compulsory three first and then compulsory four. So maybe booksellers don't buy compulsory four reference books because they think they are out of date, I guess.

But there is a way that may be faster than surfing the Internet. Ask the bookstore near your school that specializes in teaching AIDS. Even if it is out of stock, you can ask your boss to help you adjust your books or provide other methods.