Control events (like a Button's click event) occur before DataBound events (see ASP.NET Page Life Cycle on MSDN for more information). Thus, your Repeater is not DataBound yet, so its databound controls have not been initialized (they are null).
You have some options.
Preferably, you would use the Repeater's databound event to work with it's data items - since this is when you know for sure that they are initialized and populated with values.
However, you could just call "DataBind" prior to doing the processing in your Click event:
Protected Sub btnSubmit_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnSubmit.Click
rptrDivision.DataSource = yourDataSource
rptrDivision.DataBind()
For Each Item As RepeaterItem In rptrDivision.Items
' The rest of your code
End Sub
This should ensure that your controls have values.