I have come across a couple of lootable boxes that I am unable to open. It says that I need 0/1 Heyenas key to unlock it. I have yet to find a single key so far. How/where do i get these keys?
You need to get them from the key boxes in the sewers. They are fairly hard to see since they are not highlighted that well but they are common enough. Once you start looking, you will end up finding a few of them fairly quickly.