You can create tiny balls of glass in several ways. You can cut small squares of glass as small as 5mm, place them in the kiln and fire to at least a rounded tack fuse temperature.
You can do the same with frit. Make your own by smashing the glass within some container, which can be as simple as newspaper. Sieve out the finer and larger glass and put the chosen size into the kiln at the same temperature. This will give more irregular pieces than squares, so you may want to include these pieces of frit in a regular fuse firing in the spare spaces.
You can also make balls individually by putting the piece of glass on a graphite block and heating it up with a blow torch. This will round up even a rectangular piece of glass. You can put these into a fibre blanket, but it really is not necessary as the round form will contain a lot of stress that will later be removed by subsequent firing. It is possible to over heat some glass, especially opalescent, so be careful about the amount of heat you apply.