Where are the tubes of vascular plants found?

All over the body except on the cornea of the eye. Oxygen diffuses directly from the air to corneal cells to keep the cornea transparent. There are fewer blood vessels in connective tissue and bone than in high metabolic areas such as muscle cells and organ cells, but blood vessels (vascular tissue) is found all over the body.

If you mean plants, that's a different category, but xylem and phloem are the vascular tissues of plants, found from roots through stem to leaves. In woody plants, this thin layer of tissue is found right under the bark.