A friend of mine did farm Arenas in a big city with 8 players in two cars, they were hunting for 4-star raids and checking what hatched.
They spent half a day, she participated in 7 Tyranitar-raids and got really lucky, she caught 5.
For that, you need chatrooms where people share all the 4-star raids they spot, and update when it hatches. Or you need a working live map to reveal all the raids. Or you drive around the city with 3 people checking out the nearby arenas and one driver. Obviously it needs to be a big city.
I am too lazy for that, when i have time and there is a 3 star or 4 star raid nearby, i just go there, look what hatches, and hope that people show up. I did not get a tyranitar from a raid yet. The one i have cost me maybe around 160 candy for evolving and powering it up from a good larvitar.