There aren’t many books more difficult than, say, ch 12 of Athenaze and less difficult than an authentic Greek author, but this book is one of them. You can download the entire digitization of the book here:
https://drive.google.com/file/d/1Ie-qmI2dbErV5k3J0kNCi6FqWThPRf2U/view?usp=sharing
or if you just want to read the narrative which is a simplification of the Anabasis, you can read that here:
https://drive.google.com/file/d/1UX_AbvPgDZgNyZwW_M46BfK4T-YXWr7d/view?usp=sharing