Finding Others?

I think it's safe to assume that he could have repaired them but he didn't have any necessary tools to repair them properly. When he cut off his finger he had to get it repaired by the people who made him. He is capable of small self maintenance but to put back together an almost fully dismantled robot from an early era and reboot it would be extremely difficult and probably impossible for him to do alone in the wilderness etc. He was searching primarily for another robot who was as "unique" as he was. The idea that he never found one implies that there either were no others or that there were no others who could be salvaged.

Or it may be that he went back and recollected those other NDR robots with Rupert and used those pieces to construct some new personality chip for Galatea who is especially different at the end of the film.

He was looking for robots that had a developed mind like his. There was no way to develop or fix their minds after they were "gone" or "reprogrammed".