Authorized by Hanban, HSK Standard Course is developed under the joint efforts of 北京语言大学出版社 (Beijing Language and Culture University Press, or BLCUP) and 汉考国际教育科技 (Chinese Testing International, or CTI). With HSK test papers as its primary source, HSK Standard Course is characterized by a humorous style, familiar topics and a scientific course design. Matching the HSK test in all aspects, from the content, form to the levels, it is a series of new-type course books embodying the idea of “combining testing and teaching, and promoting learning and teaching by testing”. It is suitable for the Confucius Institutes in different countries as well as other Chinese teaching institutions and self-taught learners.
The whole series is divided into six levels matching the HSK test, with one volume for each of Levels 1-3 and two volumes for each of Levels 4-6, totaling nine volumes.
The best option would be purchasing them online through third-party book sellers. We recommend PurpleCulture.net, it's a Hong Kong based online store dedicated in providing Chinese cultural and educational products. They stock all of the HSK Standard Course textbooks and workbooks, and provide worldwide shipping. Alternatively, Amazon has most of the books in stock as well.
The official publisher (BLCUP) has the textbooks/workbooks in eBook format (flipviewer only for Windows PC as of now). You'd have to register for an account, then select a textbook/workbook and click on the "eBook: view" above the "Buy" button.
You might come across *unofficial* PDF files of the textbooks/workbooks across the internet, download at your own risk, we recommend buying the official books.