Where can I obtain one of the above manuals at a reasonable cost?
Honestly, there probably never was a manual specifically for that board, since it's a board that came with an OEM Gateway machine. The "manual" would have been the documentation that came with the system when it was bought new, but it's doubtful that any of it ever had much info on the board itself.
Here are the specs for it though: http://support.gateway.com/s/MOTHERBD/FIC/105553/105553sp26.shtml
And any more support for it that might exist is here: http://support.gateway.com/s/MOTHERBD/FIC/105553/105553nv.shtml