Barth is not as other worldly or anti worldly as may be supposed, given his strident and comprehensive rejection of natural theology. While the grace and love at the foundation of creation is hidden, unknown and unknowable to natural reason, it is nonetheless there, even outside of the church, not floating in some ethereal other realm. Barth elucidates this at a number of points in volumes III and IV of the Church Dogmatics (the doctrines of creation and reconciliation, respectively), yet he is ever cautious for fear of introducing some other norm for theology than Jesus Christ.
In particular, his discussion of “little lights” in IV.3 contains only large hints, no concrete examples, of how these lights are manifest outside the church. He explains his reasoning for this in a small excursus, wherein he states:
None of the concrete phenomena which arise in this connexion is as such the matter under consideration. All such phenomena are doubtful and contestable. What is not doubtful and contestable is the prophecy of the Lord Jesus Christ and its almighty power to bring forth such true words even extra muros ecclesia and to attest itself through them. 
Nonetheless, the “large hints,” as I call them, are indicated throughout his discussion and can basically be summarized as the joyful discovery of genuine love and mercy and forgiveness outside of the church, all of which are the word and work of Jesus Christ in the world. Barth even goes so far as to say that there are prophets and apostles “in different degrees” outside of the particular history with Israel and the church:
We recognize that the fact Jesus Christ is the one Word of God does not mean that in the Bible, the Church and the world there are not other words which are quite notable in their way, other lights which are quite clear and other revelations which are quite real. We may think of the prophets in the Old Testament and the apostles in the New. We may think of the genuine prophecy and apostolate of the Church. And why should not the world have its varied prophets and apostles in different degrees? …Nor does it follow from our statement that every word spoken outside the circle of the Bible and the Church is a word of false prophecy and therefore valueless, empty and corrupt, that all the light which rise and shine in this outer sphere are misleading and all the revelations are necessarily untrue. …the whole world of creation and history is the realm of the lordship of the God at whose right hand Jesus Christ is seated, so that He exercises authority in this outer as well as the inner sphere and is free to attest Himself or to cause Himself to be attested in it. 
Carl Braaten, a Lutheran dogmatic theologian, has a clear and helpful commentary on this passage:
Barth has usually been known to restrict the witness to the Word of God in Jesus Christ to the Bible and the church. Now he clearly speaks of another circle of witnesses, including words and signs and lights and revelations in the world of non-Christian religions, apart from and not dependent on the Bible or the Church. Barth’s christological thesis is not shaken by this acknowledgment of a third circle of witnesses beyond the Bible and the church. None of them can replace or supplement the one Word of God in Jesus Christ. …All other words and witnesses outside the wall of the church (extra muros ecclesia) must be measured by this one Word of God in Jesus Christ; and yet Barth is sincere about these extramural words of other religions and systems, including modern neopaganism and secular humanism. [No Other Gospel: Christianity Among the World’s Religions, Fortress Press / Wipf & Stock, p. 58]
These other words are “parables of the kingdom” to which the church must listen in its dialogue with other religions or secular thought, finding their material source and center in Jesus Christ as attested in Scripture, “although from a different source and in another tongue” (IV.3, 114-115). I like the way Braaten contrasts Barth’s approach with natural theology: “Natural theology always relies on the capacity of human reason to reach truth about God; but Barth counts on the capacity of Jesus Christ to create human witnesses wherever he pleases, even against their knowledge and will, and certainly beyond the limits of the Bible and the church” (No Other Gospel, 59).
Image: “900 Million” (Poverty Series 2) by Liseva. In light of Mt. 25, it seems that world hunger may be a good place to see Christ both within and outside the walls of the church.