Take the 6 train to Astor Place and walk east.  Astor Place becomes Saint Marks

Take the N/R train to 8th street and walk east.  8th St. becomes Saint Marks

Take the F train to Second Avenue.  Exit on the First Avenue end of the train and walk up First Ave and make a right on Saint Marks Place

Take the L train to First Avenue and walk down First Avenue and make a left on Saint Marks Place

Please note: the store is approximately the same distance (less than 10 min walk) from all the above train stops