You can still have rainbows in any Vue atmosphere (except Image based lighting), provided the sun is behind your camera and you tick the rainbow option in the atmosphere editor.
As for atmos, I'll blow my own trumpet here, I sell under my real name there as Bruno Memain, and have a few spectral atmos packs, the one called "Overcast spectral skies" has an atmo with a rainbow. But they're not voucher friendly.