The observation and conclusions that you have made are correct and without a RadSkinManager you will not be able to retrieve all of the available skins with such approach.
However, I could suggest that you try the following, more generic, way for retrieving the list of skins:
sender, EventArgs e)
> list = Telerik.Web.SkinRegistrar.GetEmbeddedSkinNames(
In general, it should not matter what control you are passing as parameter.
Hope this helps.
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