According to forms submitted to the United States Securities and Exchange Commission, the Surface tablet will become available at the same time as Windows 8 (26th October 2012).
Windows 8 Release Date Announced
At Microsoft’s annual Worldwide Partner Conference (in Toronto, Canada) Windows Chief Marketing Officer and Chief Financial Officer Tami Reller announced that Windows 8 is on track to Release to Manufacturing (RTM) the first week of August, with general availability by the end of October.