MSPSCAN.exe is part of Microsoft Office Document Imaging. For it to be present, you must have a version of Office installed with Microsoft Office Document Imaging selected during the install process.
Note that Office 2010 (Office14) does NOT have the Document Imaging functionality.
If you have Office and MODI installed, you should be able to find
MSPSCAN.exe in the folder
%CommonProgramFiles%\Microsoft Shared\MODI\1X.0\ (32-bit) or
%CommonProgramFiles(x86)%\Microsoft Shared\MODI\1X.0\ (64-bit), where 1X.0 is your Office version (10.0, 11.0, 12.0)