These are posted to www.autodesk.com/developmap.
Last version of ObjectARX for AutoCAD Map 3D which can be downloaded is 2011: http://usa.autodesk.com/adsk/servlet/item?siteID=1
Alexander - A member of my team is taking care of updating that page to include the 2012 SDK. (The direct download link on the page I quoted incorrectly bypassed that).
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