Private Sub C5_Change()
Dim cel As Range
C6.Clear
With Sheets("Stock")
.Unprotect
For Each cel In .Range("b2:b" & .Range("b65536").End(xlUp).Row)
If cel.Value = C5.Value Then C6.AddItem cel.Offset(0, -1)
Next cel
C6.ListIndex = 0
.Protect DrawingObjects:=True, Contents:=True, Scenarios:=True
End With
End Sub