RAD Controls i think were the older controls.
They were replaced with the ASP.net AJAX controls.
If you want all of them to show up in Visual Studio you have to add the Telerik.Web.UI dll to your Visual Studio toolbox.
If you right click where the other tools are, then from the context menu, select "Choose Items" then browse for the Telerik.Web.UI dll in the bin folder.
Assemblies for the most part are always located in the /bin folder.