From DeJohn's website:

Bronx:

Bronx Bookplace, Inc
2460 Grand Concourse
Bronx, New York 10458
(between Fordham Rd. & 188th st. Manhattan Store:

Hue-man Bookstore
2319 Frederick Douglass Blvd.
New York, NY !0027
(between 124th & 125th streets)

Brooklyn store:

Nubian Heritage
560 Fulton St.
Brooklyn, NY 11217

Queens Store:

Nubian Heritage
168-14 Jamaica Ave
Jamaica, NY 11432

Doesn't have anything on an e-mail adress, but try doing a search nonetheless.