Galacto-oligosaccharides are produced through the enzymatic conversion of lactose, a component of bovine milk. It is isolated from Natural Sources include human breast milk.
Some of food sources include Jerusalem artichokes, burdock, chicory, leeks and onions.
However, if you are asking because you heard it is called brain sugar and alike, I do not know of evidence relating galactose to a better brain or nervous system, that may be a myth. Also, the oligosaccharides most likely be only food to some bacteria, who produce short chain fatty acids in turn of which about 1/3 worth of the galactose calories become an energy source for the body.
What makes galactose or galactose oligosaccharides special ?
Sorry, that was galactomannan, not galacto-oligosaccharides(galactan) in coconut:
But galactomannans may be even better than galactans from several aspects such as satiety and glycemic index, the fermentation product of coconut flour has good ratios of butyrate (48%), acetate (39%), propionate (13%), though potato starch outperformed galactomannan in that regard in this pig study:
I couldn't find good information on galactan sources. Commonly included sources are legumes, and here jerusalem artichoke is shown to be a greater source though I couldn't find a study that verifies that:
Carob seeds are also a source of locust bean gum which is a galactomannan.