is there a resource where i can find the population densities for
black families living in american cities, sourced by zip code?

Hello Bx144man,

The American Factfinder will give you the precise information you require.
http://factfinder.census.gov/home/saff/main.html
Instructions
Enter the Zip Code 
Click on the word GO
Under General Characteristics you?ll obtain the number of Black or
African Americans in the Zip Code entered and the Percentage.


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Melissa Data also provides this kind of information.
http://www.melissadata.com/lookups/zipcityphone.asp
Enter Zip code and press Submit
Under Results for Zip Code, click on the link ?Zip demographics? to
obtain black population statistics


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Additional related information 

Percent of the Total Population who are Black or African American 
By State
2004 American Community Survey
http://factfinder.census.gov/servlet/GRTTable?_bm=y&-geo_id=01000US&-_box_head_nbr=R0202&-ds_name=ACS_2004_EST_G00_&-redoLog=false&-format=US-30&-mt_name=ACS_2004_EST_G00_R0202_US32


Counties within United States 
Percent of the Total Population Who are Black or African American 
By County
2004 American Community Survey
http://factfinder.census.gov/servlet/GRTTable?_bm=y&-geo_id=01000US&-_box_head_nbr=R0202&-ds_name=ACS_2004_EST_G00_&-redoLog=false&-format=US-31&-mt_name=ACS_2004_EST_G00_R0202_US30


Places within United States 
Percent of the Total Population Who are Black or African American Alone
For 70 Cities
2004 American Community Survey 
http://factfinder.census.gov/servlet/GRTTable?_bm=y&-geo_id=01000US&-_box_head_nbr=R0202&-ds_name=ACS_2004_EST_G00_&-redoLog=false&-format=US-32&-mt_name=ACS_2004_EST_G00_R0202_US31


Search criteria:
American Factfinder
Melissa Data

I hope the information provided is helpful!


Best regards,
Bobbie7