Many of these are out of print or printed in very small runs (500-1000 copies). You may find PDFs scanned by enthusiasts, but tradition holds that a physical copy obtained ethically (purchased, gifted, or inherited) carries mantra siddhi that a downloaded file lacks.
These books assume the reader has already received Diksha (initiation) from a guru. They provide step-by-step instructions: yakshini sadhana books
The Yakshini Sadhana practice is believed to offer numerous benefits, including: Many of these are out of print or
Most books reference a core list of Yakshinis. You should look for descriptions of the "Magnificent Eight" or the "Thirty-Six." yakshini sadhana books
If you are looking for the "source code" of Yakshini Sadhana, you must look into the Tantric Agamas. However, these are often written in Sanskrit code (Sandhya Bhasha) and are difficult for a layperson to decipher.