I claim the ornamental design for a target stand holder, as shown and described.
FIG. 1 is an environmental perspective view of the target stand holder; the structural elements representing the target stand forming no part of the claimed design;
FIGS. 2-5 are further perspective views of the target stand holder;
FIG. 6 is a front view of the target stand holder, the back view being a mirror image thereof;
FIG. 7 is a side view of the target stand holder;
FIG. 8 is a top end view of the target stand holder; and,
FIG. 9 is a bottom end view of the target stand holder.