How many client licenses is there for Windows Server 2008 Enterprise R2?

Contact Partner of Microsoft and ask for information on CAL (client access licenses). You can buy bundle that contains server license and CAL. (Google reveals numbers like 10, 25,...)

For licensing questions, you also can call 1-800-426-9400 (select option 4), Monday through Friday, 6:00 A.M. to 5:30 P.M. (PST) to speak directly to a Microsoft licensing specialist. Worldwide customers can use the Guide to Worldwide Microsoft Licensing Sites to find contact information in their locations. http://www.microsoft.com/licensing/index/worldwide.asp Thanks