Finalement j ai fais ca en VBA c un peu porc comme methode mais ca peut toujours servir :
Private Sub UserForm_Initialize()
Dim i As Byte, x As Byte, z As Byte, y As Byte
i = Sheets("Donnees").Range("D65536").End(xlUp).Row
For x = 2 To i
With ComboBox1
.AddItem Sheets("Donnees").Range("D" & x)
End With
Next x
For y = 0 To x - 3
For z = y + 1 To x - 3
If z <= x - 3 Then
If ComboBox1.List(y) = ComboBox1.List(z) Then
ComboBox1.RemoveItem (y)
y = 0
z = y
x = x - 1
End If
End If
Next z
Next y