!!!!!In a copy of your workbook!!!!!
Make a 2 col lookup table, with you suppliers and matching codes...I used "m1:n4" col m being supplier col n being the code. ****you will have to edit the code below to reflect your table range***
The following code assumes that your supplier names are in a continuous col, (col a) with no breaks in the data.
and no header row....
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Sub code_it()
On Error GoTo err_hit
Dim r As Integer 'row of 1st supplier
Dim c As Integer 'supplier column
r = 1: c = 1 'edit these values to reflect your worksheet layout, c is the col that you supplier is in.
Do While Cells(r, c) <> ""
Cells(r, c) = WorksheetFunction.VLookup(Cells(r, c), Range("m1:n4"

, 2, False)
r = r + 1
Loop
GoTo end_it
err_hit:
MsgBox ("Code not found for supplier " + Cells(r, c)): r = r + 1: Resume
end_it:
End Sub