I don't know where you searched that part number, but if it cannot be returned it must be a very old version of the parts program and it would stand to reason that a Blackline part cannot be found in a program that was released BEFORE the Blackline even existed.
BuonGiorno, please do not spread misinformation based on the fact that you cannot seem to copy&paste a part number. It is 71748039 and NOT 71748029.
as you can see, code ending in 29 is for for audio/CD only, not for telephone. Plus, the link you posted shows the older version of the buttons, which was replaced by the 71748029 code, basically the product shown in the link is not the same as the part number.
Plastic trims are NOT the correct color and the buttons are not flush with the trims, pretty much nothing matches
is not part number 71748029
Also, mind you there are not only light and dark trims, there are at least 4 color variations for the plastic trims.
this is the part number mentioned by OP. Sport Kit 4 is used to refer to special editions such as Blackline, Blackline III, Collezione, Q2, etc.
as far as pricing goes, not cheap at all.