First released by Desmond Dekker (US #103/UK #2 1970).
Hit album version by Jimmy Cliff (1970, released 1972).
http://youtu.be/iWrIJnWiIDo
From the wiki: “‘You Can Get It If You Really Want’, written by Jimmy Cliff, was recorded in 1970 by both Cliff and Desmond Dekker using the same backing track. Dekker’s version was the first to be commercially released, in 1970; Cliff’s original 1970 recording was later added in 1972 to the movie soundtrack of The Harder They Come.”