There is at least one guy who is making the complete chain guide assemblies. I don't have his name or contact information, but you could probably get his products from Doug Garifo at Precision Oil Pumps. Doug sells the complete assemblies (see the link below), so he might be able to get just the nylon parts and the rivets.
http://stores.precisionoilpumps.com/ford-427-sohc/FYI if you decide to buy the complete assemblies, the ones I have purchased have needed some slight mods before they are usable. On the top chain guide, the rivets stick up to high and will interfere with the front cover, so they need to be ground down a little. Also, if I recall correctly one of the holes in the lower guide needs to be enlarged just a little bit to match up to the hole in the block. This is about two minutes worth of work, so no big deal.
Hope that helps - Jay
