I have already read My crank fell off, how do I re-attach it?, but it did not answer my question.

I was biking up a hill in first gear, and I felt my left crank was a bit loose. Never having had problems with my crank before, I kept going. Sure enough, the left crank fell off.

It appears there is a square hole in the crank which the axle goes through (which is also square). This is held on by a hex bolt about half an inch long. The bolt says "CH 12.9" on the head.

Below is a picture of the crank where it attaches to the axle. Note the threads. There is supposed to be a circular piece that goes into them and holds in the bolt. Unfortunately, it must have fallen out before the crank fell off and is probably in a ditch who knows where now.

However, I believe damage has also been done to the crank. I'm not sure if you can tell from this image, but there are dents in the hole, probably from the axle. I have tried to put the crank back on the axle, but I find it incredibly difficult. I decided against a hammer with a wood block because I'm not sure if that'll make it worse.

That's my problem. Here's my question:

Is this repairable? If so, how do I go about it?