Welcome!
Possibly craigslist.
4 isn't a bad number and that's all some municipalities allow. I understand the idea behind wanting to start small but here's the reasons to start larger.
Chickens are flock animals and need friends. They can remember up to 100 flock mates. If one starts with a very small number and some die leaving a single bird alone they usually go down hill. And chickens die.
It's recommended to have at least 2 layers per family member. Once you start getting delicious fresh eggs in your own backyard, you'll eat more eggs than you do now.
After the first 12-18 months of eggs, they'll molt. They won't lay eggs during that time and after going through all that work, it's a bummer to have to go to the grocery store for eggs.
Inevitably people want to add more chickens. It is much harder to add birds to an existing flock.
I recommend getting as many initially as you can house and are allowed. It isn't any harder to tend to 10 than it is 3.