An ornamental design for a label printer media supply cartridge, as shown and described.
FIG. 1 is a front perspective view of a label printer media supply cartridge showing our new design;
FIG. 2 is a front view thereof;
FIG. 3 is a top view thereof;
FIG. 4 is a right side view thereof;
FIG. 5 is a rear view thereof; and,
FIG. 6 is a bottom view thereof.
The broken lines shown in all figures are for illustrative environmental purposes only and form no part of the claimed design. The broken lines which define the bounds of the claimed design form no part thereof.