Where do the scriptures speak of a "Church Universal" on Earth?

On the contrary, the word "church" does appear in the Scriptures, and in a meaning completely congruent with the idea of "the church universal".

Initially, it appears that congregations of "followers of the Way" - as Christians were called early on - gathered in individual houses; it wasn't until perhaps the early third century that buildings began to be set aside for Christian worship. But even in the mid-first century a regular gathering of Christians was known as a "church" - an ekklesia in Greek. Paul uses the word in his epistles:

Paul, Silas and Timothy,

To the church of the Thessalonians in God the Father and the Lord Jesus Christ (1 Thessalonians 1:1, NIV)

Paul, an apostle... to the churches in Galatia (Galatians 1:1–2, NIV)

In both of these cases (there are more), the word used is an inflection of the Greek ekklesia.

The word "church", then, is indeed Scriptural. And the term "Church Universal" (ekklesia katholike)? The specific phrase does not appear in the New Testament, but the concept of "the Church spread throughout the world" does.

Acts 8:1–3 describes the first persecution of the Church:

On that day a great persecution broke out against the church in Jerusalem, and all except the apostles were scattered throughout Judea and Samaria. Godly men buried Stephen and mourned deeply for him. But Saul began to destroy the church. (NIV)

Here is a clear distinction between "the church in Jerusalem", a local community of believers, and "the church" in general. (It is clear that it was not simply the church in Jerusalem that Saul intended to destroy; in chapter 9 he sets out to do the same in Damascus.)

More strongly, Matthew 16:18 has Jesus say: "'I tell you that you are Peter, and on this rock I will build my church." Clearly, this means "the whole community of believers throughout the world" - the meaning of "the Church Universal".

Finally, Revelation begins with Paul's salutation:

John, to the seven churches in the province of Asia: (Revelation 1:4, NIV)

With regard to this phrase, Ellicott's Commentary for English Readers states:

The churches are types and representatives of the whole family of God. Every community may find its likeness here. This much is admitted by the best commentators of all schools. “The seven churches,” says St. Chrysostom, “are all churches by reason of the seven Spirits.” “By the seven,” writes St. Augustine, “is signified the perfection of the Church universal, and by writing to the seven he shows the fulness of one.”

This is exactly what is conveyed by the phrase "Church Universal" - the community of all followers of Christ, wherever they live and worship.

There is a fundamental misunderstanding here. The original word which is translated "church" in the English scriptures did not refer to a building. It referred to the community of believers. In New Testament times there were no buildings dedicated to Christian worship so the word could not have referred to it.

The English word 'church' did not always refer to a building. At the time the scriptures were translated to English it equally referred to a group of believers, and when used in the appropriate context readers would have understood it like that. That is why the translators chose to use the word. (Clearly readers who see "The churches in the province of Asia send you greetings" would not imagine a building sending a message, still less would they imagine "the church that meets in their house" referred to a number of buildings getting together in a house).

Most uses of the word 'church' refer to believers in a particular place, such as "the church in Corinth". But there are places in scripture where it is clear the word is intended to refer to all believers (especially where Jesus uses it). Because if this, and because of other places where it is made clear that all believers in all places are somehow part of "one thing", the word 'church' (especially 'the church") is often used to mean the entirety of all believers.

The term 'church' therefore has developed to have several meanings - all believers; believers in one place; building in which believers meet. The term "universal church" is used by people who want to make it clear that they are referring to the first of those meanings.

To answer your question about where in scripture there are references to the universal church: Matthew 16:18, Acts 5:11, Acts 3:8, Acts 12:1, Acts 20:28, 1 Cor 5:12, 1 Cor 15:9, Eph 1;22, Eph 3;10, Eph 3:21-32, Col 1;18, 1 Tim 3;15 all all clearly referring to the entirety of believers.