Detail picture of the glass
If you live in Germany, you can purchase these inserts at craft stores. If you live in the European Union, this Ebay shop currently carries them. But if you live elsewhere, these may be unavailable. We have searched high and low to find shops that will sell them outside the European Union and have not been lucky yet.
A DIY action may be necessary if you would like to make your own.
Here 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.
Here three wires are used and each are soldered to the bottom
of the cup.
Here the wire is soldered across the whole bottom of the tea light cup.