Save New Combobox Value To Rowsource Range

I've got a userform with a combobox and a textbox. The combobox is populated from a dynamic range of product numbers and when a existing number is selected from the list, a respective product name appears in the textbox. These are then saved to a database sheet via command button.

My problem is following:

When a new product number is entered in the combobox that isn't on the list, I want the number & name of the new product to be saved not only on the database sheet but also on the source sheet so that the new product would be included in the combobox list when run again. Here's my code so far:


Private Sub CommandButton1_Click()

'here is the code that saves everything to the database sheet

If cboTuotenro.Value <> Range("Koodit") Then

ActiveWorkbook.Sheet("zval").Activate
Range("A1").Select

Do

If IsEmpty(ActiveCell) = False Then
ActiveCell.Offset(1, 0).Select
End If
Loop Until IsEmpty(ActiveCell) = True

ActiveCell.Value = cboTuotenro.Value
ActiveCell.Offset(0, 1) = txtTuote.Value

End If

End Sub

The problem is that I can't get the code to compare the combobox value to the range of product numbers.