Q.

The Black Cross Nurses (BCN) was an organization that developed through the influence of Marcus Garvey, the Universal Negro Improvement Association. The BCN was formally charted in 1921 as a collective of auxiliaries for the purposes of providing education, medical aid and community service. (Duncan) You can read more about this group in the following sources:

Bair, Barbara. "Universal Negro Improvement Association." Black Women in America, Second Edition. Ed. Darlene Clark HineNew York: Oxford UP, 2008. Oxford African American Studies Center. Wed Sep 25 10:19:05 EDT 2013. <http://www.oxfordaasc.com/article/opr/t0003/e0444>.

Duncan, Natanya. The 'efficient Womanhood' of the Universal Negro Improvement Association, 1919-1930. Gainesville, Fla.: University of Florida, 2009. <http://purl.fcla.edu/fcla/etd/UFE0021545>. [Chapter 4, pages 125-160 of this doctoral dissertation cover the Black Cross Nurses]

Negro World <http://dds.crl.edu/CRLdelivery.asp?tid=18223> online through the Center for Research Libraries Feb 24, 1923-1930.  The Negro World was Marcus Garvey's newspaper, and is unindexed.  Suggest that you use notes given in the Duncan dissertation to help you locate specific dates.

Macpherson, Anne. "Colonial Matriarchs: Garveyism, Maternalism, and Belize's Black Cross Nurses, 1920–1952." Gender & History 15.3 (2003): 507-27. Print. UF LIBRARY WEST Periodicals -- HQ1075.G44 [on the third floor of Library West]

If you search for "Black Cross Nurses" in OneSearch, you will retrieve many articles in the African American press from papers such as the New York Amsterdam News, the Philadelphia Tribune and the Atlanta Daily World.

Finally, Marcus Garvey's papers offer additional details:
Hill, Robert A, and Marcus Garvey. The Marcus Garvey and Universal Negro Improvement Association Papers. Berkeley: University of California Press, 1983. UF LIBRARY WEST General Collection E185.97.G3 M36 1983 or online (EBSCO)

There is an unpublished dissertation held by the library at UC Irvine on the topic, but it is not clear whether it is available for interlibrary loan:

 Leah Michelle Seabrook, “Service in Green and White: The Activity and Symbolism of the Universal African Black Cross Nurses,” (Unpublished MA Thesis, University of California Irvine, 2006)