[TrisMcC]

Vitamin D is lacking in all diets. The only meat that has any measurable D is some fish but one cannot maintain an optimal level on fish alone.

Dairy milk is commonly fortified with Vitamin D. Some mushrooms, if left in the sun, also have vitamin D.

Vitamin D comes from the sun.

[consp]

You could try free roaming chicken eggs if you do not prefer fish or mushrooms. The yolk contains quite some vitamin D.