If you just want to know the location, usbstor.INF and usbstor.PNF (amongst other usb files) can be found in C:\Windows\inf.
If yours is missing or corrupt go to C:\Windows\System32\DriverStore\FileRepository and look for one or two folders with the name ending .inf_xxxxxxxx. Use the one in the folder with the latest date and copy both the .inf and .PNF files to C:\Windows.inf.
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