Since SCCM 2012 or R2 requires installation of some prerequisites to be installed prior installing the SCCM; there are some shortcuts to do it, and not doing it while the SCCM gets installed.
Option: 1
Find/Locate for the SetupDL.EXE in your distribution or the download path you have stored in. Probably you will find it in the following folder:
X:\SCCM-Directory\BIN\X64
Now issue the following command to download the files in a temporary directory:
setupdl.exe c:\sccmprereq
Where the folder sccmrprereq directory is precreated. After issuing the command you will see that approximately 406 files will be downloaded, and it could be 384MB.
Option: 2
Download the following script and follow the instruction
SCCM 2012 R2 Prerequisite Downloader: http://gallery.technet.microsoft.com/scriptcenter/SCCM-2012-Prerequisites-1ce58746