Currently, there is no exist NAV2013R2 exams. You can find only three NAV2013 exams and NAV2009 exams. I guess, you do not want NAV2009 exams. If you want NAV2013 exams, you can try:
-Microsoft Dynamics NAV 2013 Installation & Configuration (MB7-700)
-Microsoft Dynamics NAV 2013 Core Setup and Finance (MB7-701)
-Microsoft Dynamics NAV 2013 C/SIDE Development (MB7-702)
You can find more about exams on www.microsoft.com/.../dynamics-certification.aspx
I don't know can we expect NAV2013R2 exams, because NAV2014 will come next year.