With persistence you can find just about any M14 part you need, it may take a while and a good bit of money but they are out there.
I just picked up Winchester op-rods new in the tube, cost a bunch but they are mine!
If you want to build a 100% clone your parts will have to come new from the wrap or tube ,unless marked or stamped.
Winchester rear sights were stamped OMB1,OMB2,OMB3 etc. They used WCE as a subcontractor, not as replacement parts as Art stated. TRW was know to have used Wright for example and would not have used SA. If you want real answers its best to get your info from someone other than a shooter, a collector. It may not be important to a shooter but you can bet it is to a collector.
I would suggest if you are serious about the M14 platform you consult Lee Emerson's Book, M14 Rifle History and Development
(Different). It will get you on the right track.
Oh, just about a year ago I found on gunbroker a decent Aerial for $50.00 not new mind you but in nice shape and a good example. XM25Ren