Original: Since he needed new arrangements every week for the show, his agent, John Hammond, suggested that he purchase "hot" (swing) arrangements from Fletcher Henderson, an African-American musician from Atlanta who had New York's most popular African-American band in the 1920s and early 1930s.
Simplified: Since he needed new charts every week for the show, his friend John Hammond suggested that he purchase some Jazz charts from Fletcher Henderson, who had New York's most popular African-American band in the 1920s and early 1930s.