The ornamental design for a mountingassembly for an article holder, as shown and described.
FIG. 1 is a perspective view taken from one corner of a mounting assembly for an article holder, and showing the mounting assembly supporting an article holder, said article holder being shown in phantom and not claimed herein;
FIG. 2, an exploded view taken from the bottom and one corner;
FIG. 3, a perspective view of the mounting assembly, taken from a corner;
FIG. 4, a similar perspective view, taken from above the corner;