There are a variety of bushcrafting tools that can drill holes:

It's even possible to fashion a crude brace from wood in situ. A pump drill may be a better option. (more info)

A center bit is great for saving weight. They're perfect for shallower holes, however they can also do deeper holes if you're willing to periodically withdraw the bit to clear the chips.

Another way to save weight — Power drill bits are often more burly than hand drill bits, because they have to withstand much more torque. (eg. compare these two)

The place to buy vintage hand drill bits is at flea markets or on Ebay. Vintage bits are pretty common at flea markets. Just be aware of what to look for. [1] [2]

You'll probably need to know how to sharpen a drill bit also.