Wrong, the white Rhino is the least rare of all rhinos,

there are however two sub-species:
Northern
and Southern

Southern wild Pop: around 15,000
Northern Wild Pop: around 3, the four your are speaking of have not been seen in years and are rumored dead.
Northern Captive Pop: 3

there are a total of 6 confirmed Norther White Rhinos

facts, suck them.