I guess its on their site somewhere... Until a proper petition comes out, I guess you could try, since even I can't find an e-mail adress, their message board?
I don't know if there is currently I "it can't die!" thread... But you can try searching that. There are too many threads on the Legion comics in general for me to find one that protests against the cancellation, if there is one.
Here is their news thread on the cancallation: http://dcboards.warnerbros.com/web/thread.jspa?threadID=2000146769&tstart=15&start=30
A-HA... Even better an adress!
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