Rolf,
As has been stated earlier, the drill bits are 6" aircraft drill bits. I normally get mine from Enco but have bought them from MSC when Enco was out. The other sources mentioned will work as well.
Now the important question, do you know what caused the drill to break? Not knowing any circumstances my suspicion is that the chips did not get cleared out and the drill bound up. Maybe you experienced something different. Clearing chips, even wood, is extremely important. The actual drill size bore in the guide is about 3/4" to 7/8" long. You need to clear chips every 1/8" or so.
The other thing I do is I layout and drill the stock with the barrel removed. Once I have the pin hole through the stock, I clamp the barrel back into the stock and then using a standard jobber length drill I mark (dimple) the tennon. I then remove the barrel, center punch the tennon and complete drilling the hole. The reason I do this is that I have learned that the steel chips from the tennon can work to auger out the 1/16" hole in the wood when clearing chips.
I hope this information helps. If you need any assistance please PM me and I will be more than happy to assist you. If you are missing the instructions I enclose with the drill fixture I can email you a copy of them as well.
David
