buying another used or new kit (some shops still have them in stock n now for bargain) for parts is a expensive inventory. some parts r just common wear n tear, those r the one that a bit harder to find.
below r pictures of the bumper mod (sort of mod as the upper bumperplate actually is from serpent 720, but actually it can fit directly into s400). avoid using the aluminium body post. mine r for show purpose only. i actually only use the plastic unit for both cars.
i don't think serpent still has any sponsor/partly sponsor/factory driver for s400. it's a shame as so many promises were given for this car n now it's vanishing. well, at least it'll be exotic

. going into a race without factory driver support is a bit difficult for normal racers, we don't have a setup guide in the 1st place. try n error, n end up racing it as long as it can move.
good luck.