The ornamental design for a flotation device for spectacles, as shown and described.
FIG. 1 is a perspective view of a flotation device for spectacles embodying the design of the present invention.
FIG. 2 is a front elevational view thereof; the rear elevational view, the top plan view, and the bottom plan view being identical thereto;
FIG. 3 is a left side elevational view thereof, the right side elevational view being identical thereto; and,
FIG. 4 is a perspective view showing the flotation device for spectacles in use; the broken line showing of environmental structure is for illustrative purposes only and forms no part of the claimed design.