Will wrote:
Anyone know why you can't buy diamond drills - I have a diamond saw but the
hardest drill I have is HSS Cobolt?



Because diamonds "grind" rather than "chisel".

For drilling stone, there would be no advantage to making a diamond
drill over a TCT drill and it would be a lot more expensive.

For drilling wood or steel, the grinding action of a diamond drill would
be inefficient compared with a tool that cuts ("chisels"). Now, if you
could make a solid diamond tip for a drill and put a cutting edge on it,
that would be awesome (assuming it wasn't too brittle to be of any use).