Corrected entry: When Mark had got his helmet glass cracked in the front, he had duct taped it but in the later scene he has a perfectly clear and undamaged helmet. He could not have got it from any other place as all the other astronauts had taken theirs on board the Hermes.
Phaneron
27th Mar 2018
Correction: Much like their food rations, NASA would provide them with numerous extra helmets for redundancy purposes. If one of their helmets were damaged and became unusable while on their mission and there were no extras lying around, then they would be SOL.
Phaneron ★