The proper body that trains and certifies customs brokers in the us is The National Customs Brokers & Forwarders Association of America, Inc.
Exam prep courses are available, contact them, maybe they will sell you just the manuals, and as posted above vasily showed where to download old exams from previous years.
Also Vasily, the books you posted are for Mortgage brokers not customs brokers. Customs Broker Prep Courses - Education Institute - NCBFAA
Finally, all of these answers have assumed you live in the US, if you don't please let us know which country.