If you live in Germany, you can purchase these inserts at craft stores. But if you live elsewhere, these may be unavailable. We are unable to locate any websites at the moment that sell these inserts. If we do find any, we will post the link here.
A DIY action may be necessary if you would like to make your own.
Below are two examples of the tea light inserts. Stiff metal wire pieces are bent then soldered on the bottom of the tea light cup. Then brought over the sides and curled at the ends.