ColorBrewer palettes are not available in ArcMap. There was ColorTool, a plugin for ArcGIS 9.x developed by National Cancer Institute, but as indicated in this question from 6 years ago, it was never upgraded to ArcGIS 10.
Answers to that question elicited the response to download the style file from http://codesharing.arcgis.com/?dbid=14403. However, this domain no longer appears to be maintained, and no style file is available for download.
Does anyone know of another source for this style file?
Edit: The nonexistent file is also linked to from http://www.gisuser.org.nz/tips-and-tricks, which conveniently explains, with screenshots, how to import the style file once you have it.
Best Answer
Reach Resource Center has a archive copy of a Color Brewer ArcMap style file available for download.