In the NYC area, NYPL and several CUNY schools apparently have it, see: http://www.worldcat.org/oclc/2258393

It appears to be part of the Underground Newspaper microfilm collection - see description here - you might pick up a few more holdings searching under that title.

It appears that the NYPL copies are at the Schomburg Center , including some of them in hard copy: http://nypl.bibliocommons.com/item/show/12032589052_the_black_panther (Sc +323.2-B (Black panther) Library has: v. 2-7; 1968-1972) [Also on microfilm: Sc Micro RS 103, Facsimile reprint]