KOReader can search a book on your device by filename.
Invoke a search via filebrowser main menu Search - File search or with an assigned gesture.
Wildcards ? for one and * for more characters can be used.
A search for single * will show all files.
Search string can include special characters in accordance with the Lua patterns.
Start a search from the Home folder or from the current folder. Subfolders are included.
If Show hidden files in the filebrowser settings is enabled, search results will include hidden files.
If Show unsupported files in the filebrowser settings is enabled, search results will include unsupported files.
The sorting order in the search results is the same as in the file browser.
Long-press on a file to view its full path.
Tap a supported file in the search results to open it.