Hi! I'm glad you like the icons.
Unfortunately there is no way to buy only the bonus icons. But I will contact craftpix so that they can add additional icons to their site.
Email me at prostoj-00@mail.ru what sets you have purchased so that I can send you the bonus icons
You can follow me on itch.io to receive notifications about new sets by email
I hope I answered your questions. If you have any new ones, feel free to write :)