In the The Hobbit and The Lord of the Rings series, there are many descriptions of dwarves. But there isn't any mention of female dwarves. Are there any in-universe mentions of female dwarves? If there aren't, then how do they reproduce? Is there any explanation from Tolkien?
There were dwarf women. One is mentioned by name in Tolkien's work, Dís, the daughter of Thraín II.
From Appendix A of The Lord of the Rings:
Dís was the daughter of Thraín II. She is the only Dwarf-woman named in these histories. It was said by Gimli that there are few dwarf-women, probably no more than a third of the whole people. They seldom walk abroad except at great need. They are in voice and appearance, and in garb if they must go on a journey, so like to the dwarf-men that the eyes and ears of other peoples cannot tell them apart. This has given rise to the foolish opinion among men that there are no dwarf-women, and that the dwarves 'grow out of stone'.
Dwarf-women are not mentioned in the major stories. They were few, and did not go abroad much, so they probably could add very little to the plot.