Yes, the two sentences below that you presented are grammatically possible:
(1) “There is a cat there.”
(2) “There it is the MP3,” in the sense of “The MP3 is there.”
Sentence 1 actually uses two senses of “there”—the first the so-called anticipatory “there,” and the second, the pointing “there.” By definition, the anticipatory “there” is a pronoun that carries little or no independent meaning but simply points forward to the notional subject that’s placed later in the sentence for reasons of end weight or emphasis. In the sentence “There is a cat there,” the notional subject of the anticipatory “there” is the noun “cat.” On the other hand, the second “there” in that sentence is the pointing “there”—an adjective used for directional emphasis.
Although grammatically possible, Sentence 2 is actually a run-on sentence that strict grammarians are likely to sneer at. To make it grammatically aboveboard, it needs to be punctuated in any of the following ways:
“There it is, the MP3.”
“There it is: the MP3,”
“There it is—the MP3.”
All three punctuations work but the third—the double dash—is preferable stylistically because it delivers just the right sense of pause needed by the statement.
RELATED READING:The wisdom of routinely avoiding anticipatory “there is/are” clauses
