I will show you a really good location with a generated save point to reload and get upwards of 60+ modern arrows and flares (some cash and electrical tape and deers too).
This location is called the Abandoned Film Crew Camp.
It is near geese lake, which is also the entrance to a cave. On the map, it is a little bit to the south of geese lake, and if you go there you will be bottom left of the map and it is a couple of tents and modern boxes that the arrows are in.
There is a tent that you can save and reload on so the 60+ arrows become infinite.
Be careful though, because it is on a cannibal patrol route (there is also an abundant amount of deer).