ive got the one that came with my set off LPP headers that i never used, its si/so 3"...pm me if you want pics

 

It all depends on the grade of stainless, I've seen stainless steel get surface rust that looks horrible but stay solid all of the way through. My cat back is stainless and looks horrible on the surface, but is completely solid. It is my understanding that the factory exhaust is stainless also, if it were aluminized, they'd be replacing them under warranty all of the time here in the northeast...

 

that's a good point. anyway you can get some here: http://www.magnaflow.com/02product/02flanges.asp