I have had this happen in the past, and just yesterday, it happened to me again. My solution, while some might think that it is unconventional, is to whack the side of the snow blower where the shaft is, and try again to see if it is in alignment. Yesterday, it was particularly way off, almost to the point that I could barely see one edge of where the broken shear pin was. I then whacked the other side, and checked again, and low and behold, everything was back in alignment.
It is my theory, and not supported by any scientific evidence, that the brass gear on the auger shaft will move one way or the other when you encounter something that breaks the shear pin. I know that this gear is a press fit on the auger shaft, and it is only an "interference" fit. By whacking the end of the auger shaft, the brass gear realigns itself, and allows you to install a new shear pin. I keep my augers well lubricated by pumping grease into them at the beginning of the season, and both the augers and shear pins are well lubricated. I also keep two 1/2" wrenches, a non tapered drift pin, small ball peen hammer, and a bunch of shear pins in my tractor during snow season. That way, I can change them as soon as I noticed that they have broken. I am thinking that I am going to add the heavy dead blow hammer to my traveling arsenal of tools, to keep trips back to the garage to a minimum. I must break at least 5 or 6 shear pins a season. This year I am averaging 1 per storm!