The only manufacturer of new auger bits for braces I am aware of is the Irwin 43697 set (amazon link ). It's a 13 piece set and costs a bit shy of $200 in the US. Prices in Europe are much, much more expensive, amazon.co.uk sells them for $600!

All the other sellers of auger bits for braces sell new old stock from factories closed long ago, and are rather expensive.

You can find them at antique sales, ebay, etc randomly. Sometimes they're really cheap but quality varies.

I have not had any luck using any other kind of bits in my brace, the ones intended for drill presses don't work very well at low speed. But I can't claim to have used every kind of drill bit out there, some may work better than others.