you can just take one of your other ones out and go to your nearest bomgaars or anything like it, show them the bolt and they will hook you up with a new one.
You should get rid ob those neoprene gaskets and buy the rubber w/ the steel inserts from ford. They are awesome quality and never leak. I had those on my stock 5.0 for 12 years from the factory and never leaked. When I modded the engine I put new ones back on. A little pricey but who wants to take the upper back off.