Where can I find the apron/towel worn by the America's Test Kitchen staff?
The traditional butcher's apron tie is to wrap the strings of the apron around behind one's back, then back to the front to tie.  This provides a convenient place to put a tea towel or rag.

From the photos, this appears to be what the folks in the picture have done (Becky and Chris, IIRC).  When I worked in a deli on Long Island, this is how we tied our aprons.