It's not too difficult to make a passable long hole borer from steel rod - I have one knocking around in the shop somewhere - google for instructions - you might find something. If I find it I'll pop it over.
Edit:
If I remember correctly, it's a case of cutting/grinding away half the rod down for a bit in oreder to have somewhere for waste to collect, then hardening and sharpening the cutting end , possibly into a low point with sharp on each cutting side - trial and error, but can work....... I'm sure someone on here will know.......