This work presents an efficient simulation-assisted procedure to retrieve the effective constitutive parameters of anisotropic metamaterials using the multimodal transfer-matrix method (MMTMM). The validity of the effective parameters is limited to the non-diffractive regime where p ≤ λ0, with p being the periodicity of the constitutive unit cell. Particular emphasis is placed on finding the effective refractive index and impedance, since these quantities are essential to characterize the reflection and transmission of plane waves in lens-based and other microwave applications. Expanding on previous studies, the MMTMM is generalized to deal with oblique incidence when determining the effective permittivity, permeability, and impedance tensors. A novel effective strategy is also presented to compute the effective TM and TE refractive indices and impedances. For illustration purposes, we study three anisotropic metamaterial structures: a wire medium, a stack of L-shaped particles used for polarization control, and an artificial material composed of glide-symmetric patches that can act as a dielectric of high permittivity. The proposed method is validated by comparing the scattering response of a finite stack of the composite structure with that of an equivalent homogenized slab filled with the retrieved constitutive parameters. Finally, as a design application, a matching layer implemented with homogenized stacks of patches was synthesized to match the impedance of a slab illuminated by an oblique incident wave.