Nowhere. But where does the Bible say that everything Christians believe must be found explicitly in the Bible?
Putting that aside, the reality of Jesus’ soul and divinity being present in the Eucharist is embedded in what Jesus says about the bread and wine becoming his body and blood. His soul and divinity are present by way of concomitance (see Summa Theologiae, III:76:1).
For example, on account of the real connection between his body and blood, his soul is also present with the body under the appearance of bread because he is a living body (see Rom. 6:9). The Eucharist is not the dead flesh of Christ. It is his living and glorified body. Similarly, under the appearance of wine, Christ’s body and soul are present with his blood because of his living presence. To speak of Christ being present in the Eucharist “body, blood, and soul” signifies that he is present fully in his human nature.
His divinity is present on the ground of the Hypostatic Union (union of human and divine nature in the one divine person, Jesus). Because the subject of the Eucharist is a divine Person, the Second Person of the Blessed Trinity, we must say that Jesus’ divinity also is present.
So, even though the presence of Jesus’ “soul and divinity” is not expressed in Scripture in relation to the Eucharist, it is there implicitly by way of association with the presence of his living body and blood.