The ornamental design for a mountableguitarpickcase, as shown and described.
FIG. 1 is a front, left side perspective view of the mountable guitar pick case;
FIG. 2 is a front elevation view of the mountable guitar pick case;
FIG. 3 is a rear elevation view of the mountable guitar pick case;
FIG. 4 is a left side elevation view of the mountable guitar pick case;
FIG. 5 is a right side elevation view of the mountable guitar pick case;
FIG. 6 is a top plan view of the mountable guitar pick case; and,
FIG. 7 is a bottom plan view of the mountable guitar pick case.
The broken lines shown in FIGS. 2, 3, and 5 are for the purpose of illustrating a patch that forms no part of the claimed design. The remainder of the broken lines showing stitching do not form part of the claimed design.