Hi Pete - many thanks for your very kind comments. I get nut and bolt and rivet castings from Cambrian Models - http://www.cambrianmodels.co.uk/16intropage2.html
They are supposed to be for 16mm scale, but bolts and rivets come in all sorts of sizes ...
As for loco drawings - I use Google Images to search for what's online and often use photos as a basis for a 'working drawing'. Also, many preserved NG lines have web sites with useful info.
Hope this helps