What about sources of differences in ethics between people, companies and nations, where would I find this information?
When you talk about sources of ethics, you need to realize that there is no one source of ethics. The best way to understand sources of ethics is to look at religion and the sociology of knowledge.
First, religion is always a source of ethics. Some may not like this answer, as religion often gets the short end of the stick in academic circles. However, religion has shaped ethics in many ways. The West has been shaped by Christianity, even if the country is now secular, like France and Germany. The Middle East has been shaped by Islam. So, we can say that a source of ethics for the individual, companies and countries is religion.
Second, a basic insight from the sociology of knowledge is that all knowledge and ethics are socially conditioned. So, what is true or right in one place might not be in another place. From this perspective ethics is a product of society. Or we can say that a source of ethics is society.