Hi Nathan,
I trust you are aware of the following excellent website:
http://www.s2ftracker.com? Moreover, checking a photo database such as airliners.net can also be a great help.
As was mentioned by
kalamazookid, there are (at least) two C-1 Traders on the airshow circuit: N778SR (BuAer 136778) and N189G (BuAer 146044; returned to the air in 2013 following its forced landing in 2002). I photographed both in the air in 2013.
The one
bonzo referred to must be N81389 (BuAer 146049), which is owned by a company called 'Aviation Business Corporation' from St Louis, MO. Apparently it is having its interior redone, and will be followed in the restoration queue by the S-2 that is/used to be at Akron/Canton, OH.
According to s2ftracker.com and in addition to
flightsimer's information, N475AM (BuAer 136781) will be kept airworthy (at least for the time being).
In addition (cf.
http://www.s2ftracker.com/usatraders.htm) there are a number of airframes that are potentially airworthy or are being restored and that I hope to see return to the air at some stage.
According to
http://www.s2ftracker.com/usatrackers.htm there at least five S-2 Trackers under restoration to airworthiness in the USA alone (one owned by the Collings Foundation, one owned by Tom Reilly, the aforementioned ex-Akron/Canton one, and one in Nevada and in Alabama each). I'd be as happy as you if I could get to see/photograph each one of those in the air!
Unfortunately I don't believe we'll ever get to see an E-1 Tracer fly again

Roger