Hi,
This is a follow on request from a ticket raised where it was stated this feature isn't available and there is no work around.
When you hook a RadCombobox to a RadClientDataSource, which returns a paginated set of results along with a count of total number of records, the RadCombobox should display the "Show More Results" box along with the text stating "Items 1 - x of y" as all that information should be able to be calculated from the data returned.