Many of Stein’s publications are available online at The Internet Archive. Go to https://archive.org/search.php?query=aurel%20stein
Ruins Of Desert Cathay and many of Stein’s other works are available from Amazon.com, including a Kindle edition of “Ruins - Volume I” for $2.99. A paperback edition for $26.50 per volume is available at: https://www.amazon.com/Ruins-Desert-Cathay-Aurel-Stein/dp/0486253511/ref=sr_1_16?s=books&ie=UTF8&qid=1547396793&sr=1-16&keywords=aurel+stein
Ruins Of Desert Cathay is an almost day-by-day recounting of his two-year long 1906 expedition to “western China” — what is now known as China’s Sinkiang Province. This is a work which you can open on almost any page and immediately become captivated. Stein kept meticulous daily records of his work and travels, which he would write up in his tent at night, no matter how harsh the environment around him. And his writing is first-rate English prose in a personal style that is modest and professional, conveying both the realities of life on the trail and the methods of a careful archeologist. The link below takes you to online copies of the original edition of Ruins.
Ruins Of Desert Cathay Volume I is at: https://archive.org/details/in.ernet.dli.2015.184786
Ruins Of Desert Cathay Volume II, see: https://archive.org/details/in.ernet.dli.2015.173310/page/n3
Photos from Ruins of Desert Cathay. High-quality reproductions of Aurel Stein’s own photos from the above book are available on this website run by the Xenophon Military History Group. The reproductions in the online and pdf texts of Ruins unfortunately don’t do justice to Stein’s photography, which makes this website invaluable. His photos document not only the awe-inspiring landscape and archeological findings on his trip, but also the Asian staff who made his success possible and the many officials, travelers, casual laborers and local people he met and benefitted from along the way.
See http://www.xenophon-mil.org/china/centralasia/ruincathyphotos.htm Note: Click on the blue dot next to each description to view the photograph.
Sand-Buried Ruins of Khotan is the record of Stein’s first archeological, a one-year effort beginning in 1900 that launched his career. It was a pioneering trip in itself but also paved the way for his spectacularly successful 1906-1908 expedition.
https://archive.org/details/in.ernet.dli.2015.16671/page/n5