I've swapped augers before on the Searsasaurus.
Here it was with the 32" 3 stage
Here it is with the 26" 2 stage
I suspect that anything easily identifiable as swapable with have the same basic dimensions, just a different width. You may be able to use a different vintage piece or different brand of auger.
I really think the easiest route would be to sell what you have and replace it with something different.