Buy it at Amazon or Barnes and Noble. 

Amazon:

Book 6 -  https://www.amazon.com/Rochanit-Engineering-Woodson-Securities-Investigations-ebook/dp/B0GX2YJP1L/ref=sr_1_2?crid=28R6LEJJC7P4Y&dib=eyJ2IjoiMSJ9.DCQg4XgyizOusR7iy3oTyxb4gAYQuPt2snMXa8S7lexcLVNOQhOhl-rrZMCFQYUTYa2T4Fo7sApUuZ8CWLFgS3S1buuxJaWtYmFTJ-q1N0vd3CppFcNOCDoQkfUnxsSCa9_gIhaZdv2c5OharC971ZyHEivx9afDRKxNSFR1LNI.kmNgANNbVY_m8tWLfpmDgXVXijk9EUo6tA6VROQDb3w&dib_tag=se&keywords=christina+baca&qid=1780356992&sprefix=christina+baca%2Caps%2C150&sr=8-2

Trilogy 4, 5, and 6 - https://www.amazon.com/Rochanit-Engineering-Woodson-Securities-Investigations-ebook/dp/B0H3DPXYX6/ref=sr_1_1?crid=28R6LEJJC7P4Y&dib=eyJ2IjoiMSJ9.DCQg4XgyizOusR7iy3oTyxb4gAYQuPt2snMXa8S7lexcLVNOQhOhl-rrZMCFQYUTYa2T4Fo7sApUuZ8CWLFgS3S1buuxJaWtYmFTJ-q1N0vd3CppFcNOCDoQkfUnxsSCa9_gIhaZdv2c5OharC971ZyHEivx9afDRKxNSFR1LNI.kmNgANNbVY_m8tWLfpmDgXVXijk9EUo6tA6VROQDb3w&dib_tag=se&keywords=christina+baca&qid=1780356932&sprefix=christina+baca%2Caps%2C150&sr=8-1

or Barnes and Noble

Book 6 - https://www.barnesandnoble.com/w/rochanit-engineering-and-woodson-security-investigations-book-6-christina-baca/1150297264?ean=2940185151358

Trilogy 4, 5, and 6 - https://www.barnesandnoble.com/w/rochanit-engineering-and-woodson-security-investigations-trilogy-christina-baca/1148783050?ean=2940185151440