Here is a link to Sara’s review complete with all of the links: http://plumfieldandpaideia.com/cs-lewiss-space-trilogy/

You can purchase the Space Trilogy books at BookShop.org - a nonprofit online book vendor which supports bricks-and-mortar bookstores and libraries. 

Out of the Silent Planet:
https://bookshop.org/a/86509/9780743234900

Perelandra:
https://bookshop.org/a/86509/9780743234917

That Hideous Strength:
https://bookshop.org/a/86509/9780743234924