Mountain Coati (Nasua nasua montana)

These two mountain coatis are separated from other coatis.

very interesting colouration, any idea where they originate from?

From what I have seen, the darker colored coati are usually from the southern Brazil/Argentinian area.

The standard South American coatis in southern Brazil and Argentina aren't much darker than the coatis we frequently see in zoos. Indeed, the specimens most frequently seen in zoos originate from two separate regions: The Guianas (nominotypical), and southeastern Brazil and adjacent Argentina (subspecies solitaria and spadicea). They've been mixed so much in captivity that I doubt it would be possible to separate these today in European and North American zoos. All are just maintained at species level. However, much darker coatis, sometimes mostly black, are found in the western Amazon and Nasua nasua montana is from this exact region: The Amazon and adjacent Andean foothills in Peru extending at least as far east as Rondonia. These specimens are fairly typical, but like most subspecies it is quite variable in color.
I guess you could call them mountain coatis based on their scientific name montana, but most of their range is lowland and this name also leads to easy confusion with the "real" mountain coatis Nasuella.