You can start with the free ones from Warren and depending on your DAW there are probably already some on board.
Hm, samples played with rods, sorry, don't know were to get those, but you could make some on your own.
As for the last question, it depends. I'm recording a cover of a pop song with some student at the moment where in the original there are huge amounts of snare samples on 2 and 4 only, but in fills and the like you only hear the recorded drums.
If the grace notes are important for the feel of the song either use samples (which I probably wouldn't do), make them more audible with compressors so you can add samples on the louder notes or not to use samples at all.