To implement the Accordion control, you have 2 possibilities:
1) Either implement it in C#/XAML. For example, you can see the code of the open source Silverlight Toolkit.
2) Or, directly use a JS-based 3rd party library such as Kendo UI Core to do it. For this, please wait for Beta 11 (expected before the end of the month), which will include the ability to import the TypeScript Definition of Kendo UI Core. We will post some samples of how to use the Kendo UI Core controls in the coming weeks.