Old Bike. New wheels.

My bike frame is old and the axel dropouts are smaller than the modern equivalent.
So I got a puncture in my old rear tyre yesterday and thought I might as well just replace the wheel with the new one I have.
Unfortunately due to the difference in axel bolt sizes I'm required to file down the dropouts. Found out that it's the hardest steel ever! I only have a crappy file :(
What should I do?

I can't live without my bike! I've ridden it everyday since returning to the toon and now I'm condemned to snail pace walking. Boooo.