Hello mastmnds
I don't know of any software, but I have tried a few ideas along this line myself, and the best I have created so far is this:
I work in an open plan office and I am quite friendly with the admin staff (no not that friendly unfortunately), so if I want to find a good typo name, what I do is ask several people to type the original DN into their wordprocessor followed by the return key as fast as they can (and without correcting errors or looking at the screen) for two or even three pages then save the file to disk. This gives you a list of between 50 to 100 type ins of the DN including any typos. Then paste this info into a spread sheet and get the next person to do the same and so on. Then sort the final version of the spreadsheet into ascending order and look for the most common typo - you can even set up a macro to do it for you. If you do not work in an office environment then ask your friends.
This way you get an idea of which typos are the best and the frequency by which they occur and if the frequency is high enough for your requirements. You can then extrapolate what you can expect to get through typo traffic by how popular the original DN site is.
I tend to find that as most people are right handed, that the more typos occur (on average) on the left of the keyboard and tend to be the keys that are pressed with the little (pinky) finger or third finger, and that the key below and to the left of the target is sometimes the most common.
But be aware of TM problems, some people and large companies get away with this and some don't.
And before anyone shouts at me that this is the appraisals section, I am only answering the question.
Tricky