There is mention of them (cows which can be milked at any time & they give as much milk as one likes) in Krsnaloka. The Lord keeps many such cows, which are called surabhi. It is stated that the Lord is engaged in herding surabhi cows. BG 1972 purports

Expressions researched:
"there is mention of them in Kṛṣṇaloka. The Lord keeps many such cows, which are called" |"surabhi" |"It is stated that the Lord is engaged in herding the" |"cows"

Bhagavad-gita As it is

BG Chapters 7 - 12

In Kṛṣṇaloka in the spiritual sky there are cows which can be milked at any time, and they give as much milk as one likes. Of course such cows do not exist in this material world, but there is mention of them in Kṛṣṇaloka. The Lord keeps many such cows, which are called surabhi. It is stated that the Lord is engaged in herding the surabhi cows.

BG 10.28 (1972), Translation and Purport

Of weapons I am the thunderbolt; among cows I am the surabhi, givers of abundant milk. Of procreators I am Kandarpa, the god of love, and of serpents I am Vāsuki, the chief.

The thunderbolt, indeed a mighty weapon, represents Kṛṣṇa's power. In Kṛṣṇaloka in the spiritual sky there are cows which can be milked at any time, and they give as much milk as one likes. Of course such cows do not exist in this material world, but there is mention of them in Kṛṣṇaloka. The Lord keeps many such cows, which are called surabhi. It is stated that the Lord is engaged in herding the surabhi cows. Kandarpa is the sex desire for presenting good sons; therefore Kandarpa is the representative of Kṛṣṇa. Sometimes sex is engaged in only for sense gratification; such sex does not represent Kṛṣṇa. But sex for the generation of good children is called Kandarpa and represents Kṛṣṇa.