I've had such a hard time locating these! I've only been able to make my own in the past by filing down a 6-sized hex bit, but they've never fit or worked very well.
These security bits are being used on an increasing number of products;
Price and Availability: I used to sell these, but demand has been too low to keep them in stock. I have located another supplier where you can buy your own. http://mcmaster.com/ and search for "Triangle Power Bit". Prices are $2.75 to $3.67 per bit. A full set will cost $13.76 + tax, S&H.