The ornamental design for a post for bath accessory, as shown and described.
FIG. 1 is a bottom, front, and right side perspective view of a post for bath accessory showing my new design;
FIG. 2 is a bottom plan view thereof;
FIG. 3 is a top plan view thereof;
FIG. 4 is a left side elevational view thereof;
FIG. 5 is a right side elevational view thereof;
FIG. 6 is a front elevational view thereof;
FIG. 7 is a rear elevational view thereof; and,
FIG. 8 is a top, front, and right side perspective view of a second embodiment thereof, with the broken line disclosure of a towel bar being for illustrative purposes only and forming no part of the claimed design.