So you are a passenger on the Three Caballeros hype train, but you are unable to find the original Disney classic The Three Caballeros (1944) movie in any retail stores or online?
In February 2018, the Disney Movie Club exclusively started offering a 2-Movie pack featuring both Saludos Amigos and The Three Caballeros. The blu-ray release celebrates the 75th Anniversary of Saludos Amigos, and it is the first time that either of these Disney Classics have been available on blu-ray.
So at this time, the only way to own these movies on Blu-ray is through joining the Disney Movie Club:
https://disneymovieclub.go.com
This release does not come with digital copies.