The 1919 Mercury Dime has one of the largest mintages in the series. It's mintage is over 35 million. Several other dates have mintages under 5 million just to illustrate where it falls in the mintage figures.
There are probably tens of thousands of examples that exist in circulated condition. In Uncirculated condition, there are probably also a few thousand examples that have survived. MS66 examples or higher are very scarce. MS67 examples are even scarcer. Anything grading higher than MS67 is rare.