www.proto87.com They supply 1:87.1 true scale stuff. They have very nice handlaying track supplies for prototype track as well as wheel sets, couplers and so on. I'm working on trying to convert over to Sergent couplers. That is as prototype as it gets.
For a quick treatise on the various scales check out this site. http://www.nmra.org/beginner/scale.html
Of course they don't show all of the many scales associated with G GAUGE!