Sometimes we just cant find drivers for those unknown devices or the process is a pain in the butt. Here is a solid way to do it with out using 3rd party programs and has always been more reliable and convenient.
1.) go to your device manager > right-click on the unknown devices properties > click on "Details" tab > click drop down menu > select "Hardware IDs"
2.) write down both "VEN" and "DEV" numbers. heres an example:
Lets say this device is Unknown
Vender number: 10DE
Device number: 0611
3.) go to this website http://www.pcidatabase.com/
> where it says "Vendor Search" type in the vender number > click search
4.) In the search results click the relative vendor to get to next webpage > on your keyboard press "CTRL + F" and type in the device number.
5.) This should now provide you with all the information you need to find the correct driver for your unknown device.
Chip Number: G92
Chip Description: NVIDIA GeForce 8800 GT