My choice for drill bits are tool suppliers for aviation. Due to the amount of drilling that takes place, aviation tool supply stores carry some of the best drills you can find, including left hand drill bits that are great for removing broken bolts and fasteners.
https://www.panamericantool.com/
https://www.yardstore.com/
https://www.aircraft-tool.com/
https://www.browntool.com/Listview/t...3/Default.aspx