You can find many different size diamond coated drill bits at
http://www.ameriglas.com/ however, they are very expensive. i bought mine and it cost me about $100 to buy two different size drill bit. however, it is well worth it in the end. it beats paying petland about $150 more to drill about 5 hole for me. just a suggestion.. also don't make the same stupid mistake i did... RUN LOT AND I MEAN LOTS OF WATER whill drilling. i was drilling my tank and all i needed was one more hole. i pretty much didn't run enough water and on top of that i was drill right under the sun with a black paint on the glass.

good luck!!
willie