The burner tube isn't sold separately. It comes with the wires for the piezo push button, right? It's my guess the wires are longer on non-SS Performers but that the burner tube is actually the same.
Either way, both assemblies should be available:
SS:
http://www.ereplacementparts.com/burner-assembly-p-1477476.html2005-(to 2012):
http://www.bar-b-que.com/brands/weber/burner-weber-performer-grills-83725-10469/What's interesting is what that place says:
"This is the burner, igniter and mounting bracket for WeberŽ PerformerŽ grills listed as 2005 and later (with the thermoplastic work area). We ordered this unit for grills before 2005 and this is what they sent us, and it fit one of our member's grill with the stainless work area, so it likely replaces both the newer and older grills."
That would make sense if the only difference is a longer wire on the later one ... the piezo mount locator is farther away from the kettle on the plastic table Performers.
Your tube has holes in it, or just looks bad? Gotta make sure you vacuum it out, remove all cobwebs etc. And the tiny orifice on the brass fitting on the end of the hose must be clean for good flow. And of course the piezo should be/can be tested for spark. If you already have a regular 20lb tank it can just reach the hose if you need to test the gas function.