Indeed, the feature is not available in the Xamarin.Forms Calendar control. I have logged a feature request on your behalf and you can track its progress on the following link from our Ideas & Feedback portal - Calendar: Add multiple and range selection modes
. I have also added some points to your account for the suggestion.
In the meantime, as the feature is available for the iOS and Android native controls, you can consider creating custom renderers and eventually use this mode for the different platforms. Here is an example of Custom Calendar Renderer
and the features on the different platforms - Android Range Selection
, iOS Range Selection
Do you want to have your say when we set our development plans? Do you want to know when a feature you care about is added or when a bug fixed? Explore the Telerik Feedback Portal
and vote to affect the priority of the items