https://blendermarket.com/products/shape-key-collections

Organizing shape keys used to be a nightmare because you couldn't give them a folder structure in native Blender.  This is where Shape Key Collections saves the day and allows for full control over your shape keys. Bring structure to the chaos, a folder structure, that is.  With this new management system you can rename and organize which shape keys go in which folder and subfolder, including the benefit of subfolders for full tidiness and ease of use.