David Akers (1975/88): The 1868 is not as rare as the 1867 nor is it quite as rare as the 1866. However, it is still very rare in any condition and compares closely in overall rarity to the 1857, 1859, 1860 and 1862. I have not personally seen or heard of an uncirculated piece.
David Hall: As far as I know there is only one known mint state coin, a PCGS graded MS62. When I put my set of $10 Liberties together (2005 to 2010), I had to settle for one of the few AU58 examples. In other words, this issue is another of the many early $10 Liberties that is either unknown or virtually impossible to obtain in mint state.