We study X-ray fluorescent emission and monochromatic scattering from the surfaces of asteroids and other atmosphereless solar-system objects using numerical Monte Carlo simulations. X-ray observations allow the assessment of the elemental composition and structure of the surface. We assume that the model regolith consists of close-packed spherical or irregular particles with a certain size distribution and that the particles are uniformly distributed within the regolith model. Here we concentrate on the monochromatic scattering component and assess the applicability of scattering methods based on the geometric-optics, anomalous-diffraction, and physical-optics approximations. We then simulate the monochromatic X-ray scattering from regolith surfaces in order to better the understanding of the contribution of illumination-angle-related phenomena on the signal obtained from, e.g., orbiting platforms. We present the first results and discuss the applicability of the methods to interpretation of future asteroid and Mercury mission X-ray data (e.g. BepiColombo).