Who was the wife of Vamana, the Avatar of Vishnu?
The information is scarce and Vamana is described as a Brahmachari, unmarried, when he eked alms from Mahabali.
So there is a general assumption that, having been called as Brahmachari, he could not have married.
There is also the general rule, according to Puranas, that Vishnu is never separated from His consort, Vishnu, even in His Avatars.
I have written on the wife of Parashurama, who is an Avatar of Vishnu and his marital status is not generally known.
Vamana had a wife, Padma.
‘For in like manner as the lord of the world, the god of gods, Janárddana, descends amongst mankind (in various shapes), so does his coadjutrix Śrí. Thus when Hari was born as a dwarf, the son of Adití, Lakshmí appeared from a lotus (as Padmá, or Kamalá); when he was born as Ráma, of the race of Bhrigu (or Paraśuráma), she was Dharańí; when he was Rághava (Rámachandra), she was Sítá; and when he was Krishńa, she became Rukminí. In the other descents of Vishńu, she is his associate. If he takes a celestial form, she appears as divine; if a mortal, she becomes a mortal too, transforming her own person agreeably to whatever character it pleases Vishńu to put on.
Vishnu Purana, Chapter 9