I’ve heard you are obligated to donate to a charity if you are unable to find someone to repay them for damages. Is that true?
Not exactly, You are required to restitute your sin which actually is against God and mankind. Many sins if not most (really all) can never be reversed. So your restitution is really to God but delivered through human means. So your restitution is alms of any kind which allows you personal retribution. This means your restitution must exceed your sin. Giving money to charity is only one forum of restitution.
see this thread