We experimentally study the optical emission behavior of a linear array of dielectric microspheres with gain. The microspheres are randomly arranged and well-separated, and can only couple via radiative modes. We observe resolution-limited, ultra-narrowband modes in the longitudinal emission, which constitutes collective lasing from the entire array, inferred from the observation of a lasing threshold. The lasing modes show wavelength selectivity, wherein the lasing probability is large only in specific frequency bands while being inhibited at other wavelengths, a behavior which is independent of the degree of configurational randomness. Analysis of the frequency bands indicates the participation of Fabry-Perot resonances of the individual microspheres in the collective emission.