You can also use optilocks if you wish, you just need to get the optilock bases with the picitinny fitment, these bases are available new, blued at around £90 and in stainless at around £125, then match them up to the appropriate height optilock rings (either low or medium height).
You very rarely see these picitinny bases on the second hand market however.
You very rarely see these picitinny bases on the second hand market however.