The ornamental design for a clip-on air gun holster, as shown and described.
FIG. 1 is a front, perspective view of my ornamental design;
FIG. 2 is a front view of the ornamental design of FIG. 1;
FIG. 3 is a back view of the ornamental design of FIG. 1;
FIG. 4 is a left side view of the ornamental design of FIG. 1;
FIG. 5 is a right side view of the ornamental design of FIG. 1;
FIG. 6 is a top view of the ornamental design of FIG. 1;
FIG. 7 is a bottom view of the ornamental design of FIG. 1; and,
FIG. 8 is an environmental, perspective view of the ornamental design with an air gun attached thereto.
The broken lines disclosed in FIG. 8 depict environmental structures and form no part of the claimed design. The break lines shown in the drawings indicate that no particular length is claimed.