Any device driver can be a tricky thing to track down. You may be able to find some versions of it, but chances are they're incorrect for your system. Microsoft mouse drivers are no different, but they don't have to be as hard to get as they once were.
As a computer technician one of the biggest error fixes I face is people having the wrong, out of date or faulty driver. By simply making sure they're using the correct driver the device needs, I've fixed more computers than I can remember. They are the cause of some of the most common PC errors today.
Now, the biggest problem with searching for Microsoft mouse drivers, or any driver for that matter, is just how tedious it can be. You can spend a lot of time with a search engine, and then wade through page after page trying to track down the driver you need, but there are so many versions and so many that are only compatible with certain systems, finding the correct one is far more trouble than it's worth.
One of the programs I use in the shop that greatly simplifies this is an automatic driver program. Not only is it useful in tracking down the right driver for the machine I'm looking for, but it also allows me to scan and see if there are any out of date or broken drivers currently present.
These programs are designed to make standard driver maintenance a breeze. They're very quick, easy to use and only cost a fraction of what you would pay to bring your computer into a shop for repair.
Microsoft mouse drivers are just one example where automatic driver software could really help, but at the end of the day it's your choice whether or not you want to buy a commercial license. However, what is fair to say is that automatic driver software really takes the guesswork out of keeping your PC and its devices up to date with the correct, and official drivers you need.