In recent years, breakthroughs in the GAMMA-10 tandem mirror device and new designs such as the Kinetically Stabilized Tandem Mirror have renewed enthusiasm for investigation of mirror plasmas. With a discrete eigenmode solver and shooting code we calculate kinetic Alfvén waves in a model GAMMA-10 experiment, and then examine the nature of the spectral gaps. We validate the results of these calculations by comparing with magnetic probe signals recorded in the LAPD as a function of frequency of the antenna and the axial position.