http://www.pacmodels.com/ and http://www.redfroghobbies.com/ have decent selection of metal tracks.
Workable tracks are tracks that are lined together and function like real tracks as opposed to ones that are glued and one piece.
DS are not sold alone by Dragon,but many modeles don't use them and are willing to sell or give away.
It's hard to find one stop shopping for everthing though,