I/O shield for the Intel® Desktop Board D975XBX is C94243-001. This can be found at: http://click.intel.com/
I/O shield part numbers can found here: http://www.intel.com/support/motherboards/desktop/sb/cs-009031.htm
Thanks for the links. The problem is that according to the Intel site, the rear i/o shield of the Intel is D975XBX motherboard is "unavailable". Hence my original questions.