In the winter Quinta_Essentia, where there is a distinct lack of sunlight, and who exactly wants to sunbathe in the freezing cold? I take supplements, but less so or not at all in the summer months, where I do have the chance of full body sun exposure............yep even in the good ol' UK no less.!! What most Americans believe I think to be the land of Fog and constant rain!!!
So in the winter months I think it is essential to supp-le-ment with D3, using a quality source.
I think you have exhausted the possibilities, although Vitamin D in milk I believe is fortified, although I could be wrong here.