A pack of five assorted I/O shields can be bought from
http://www.pcpowercooling.com. They refer to them as "templates" for some reason. It's possible that server mainboards use I/O shields that aren't the same as the ones for PC's.
I assume that "CPU Retention brackets" are what are called "Universal Retention Modules." URM's can be bought online. The trouble is that Intel's are probably a little different than Soyo's or Asus's. You can run tie-wraps, aka zip ties through the holes for the URM's on the mainboard, then up and over the CPU's PCB or Slocket. These hold the processor in place better than most URM's do.
As long as the square end of the two tie-wraps that must always remain on each end of the Slot 1 slot of the mobo are too big to ever slip through the holes for the URM to the upper side of the board, you're in business. You must also prevent them from falling out of the mobo on the under side. If they do, you gotta remove the mainboard and re-thread them through the bottom of the board. Ugh!