The ToolStrip is not a Control, it is a Component (it appears in the component tray at the bottom of the form). Components do not trigger validation (they do not have the CauseValidation property that controls have).
An event being a Sub as any other, you can call it. The solution is thus to call the validation event procedure from the Click of your ToolStripButton.
Private Sub ToolStripButton1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles ToolStripButton1.Click