The most reliable source is the Origami Tanteidan Magazine back issues. Several volumes (specifically #80, #95, and #112) feature Hayashi’s flowers. You can purchase PDFs of these magazines directly from the Tanteidan website. While the interface is in Japanese, search for "Hayashi" to find the specific issues containing flower diagrams.
For serious collectors, here is how to build a legitimate digital library of Hiromi Hayashi’s flowers: origami flowers hiromi hayashi pdf