Here is an excellent, short video about drilling glass. It is specific to "sea glass" - but the principle is the same. If you have been experimenting with fusing, or off mandrel work, and would like to drill a hole - this is how.
The phrase "let the drill do the drilling" is really important - let the drill do the work, instead of leaning on it and trying to force the drill through.
You could make your own "sea glass" by melting up chunks of scrap glass, and then annealing them, and then etching, sandblasting, or tumbling them. There is an entire community of people out there who would consider that statement to be blasphemy, but "sea glass" is broken glass bottles tumbled in salt water and sand. Mostly beer and wine bottles, fallen off boats. Hence the mostly clear, brown and green. Some blue - vodka, and the occasional red piece, a broken port running light.