Is there any one place where it is listed? If yes, can we list it here so that it os archived for eternity here?
UPSC website has the keys as far back as 2014 only.
2013 key- https://iasexamportal.com/ias-pre/answer-key/2013
2012 key- https://www.insightsonindia.com/wp-content/uploads/2013/05/csp2012_p1_ans_keys.pdf
2011 key- https://www.insightsonindia.com/2012/06/09/upsc-declares-official-cut-off-and-answer-keys-for-civil-services-prelims-csat-2011-examination/
I'll save you guys some time. I marked the official answers in the question paper pdf a couple of days back. Referring that straightaway should suffice IMO. Link is attached below.
2011- https://drive.google.com/open?id=1ZsY9wzhzeGOlCaOC_0P3PdYMQ_DHEqm9
2012- https://drive.google.com/open?id=1GYKhMGNN0yXFGVZSzA7F1nGSO5f-UxqQ
2013- https://drive.google.com/open?id=1aC0KuzOY-3FIfITz28Y_i0I7b78c3GTT