You can use the Toolbox Configurator in order to set up the Telerik controls in the toolbox. You can find more information on how to use it in the following article:
The option that Shinu suggested will work too, but you won't see the Telerik assemblies in the 'Add References' window (telerik3.png).
Hope this will help. Let me know if you need further assistance.
All the best,
the Telerik team
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