The classic of tea, maybe you can find a fine English translation online for free. This book was written long before the time intellectual property right existed, and most people could get Chinese versions for free. I'm sure there are English tea enthusiasts who have translated it for free too.
All the Tea in China, my problem of this book is reflected by an Amazon comment made by another reader - the author of this book didn't make it clear whether this book is a non-fiction or historical romance. A lot of deliberate details of the stories are entirely based on Robert Fortune's own personal writing, which I suspect is very much historical romance - I won't blame him on it... who doesn't want to describe himself as a hero when he sits down to write a memoir at an old age?
But using these stories as facts in a modern book generates a problem.
A basic deviation from reality is that China never forbade export of tea. Tea was introduced to Japan and Korea a thousand years earlier than Robert Fortune's action. Why wouldn't Japan and Korea count as tea cultivation out of China, until the tea was under the control of western colonists? Robert Fortune had to spy on tea because he was from a then- enemy state that first exported banned drug (opium) to China and later on brought up a war against China blaming China for refusing to importing opium. Robert Fortune had to disguise himself basically no matter what he did in China, and the disguise was not just because tea was some sort of guarded treasure.