Some of the best S4S that I've gotten are simply through the connections I've made through IG. Find an account that is similar to yours, and propose some mutual benefit.
You can find them easily using hashtags. I.E you're a car account, so you look up #fastrides in IG, then just scroll through. Check out the accounts that look interesting and shoot them a dm.
Within an hr you could have as many leads as you want, the more you have the more chance of someone saying yes to the S4S. Only thing you have to be careful of is copying and pasting the same message and sending them to a ton of people back to back. You don't want to get temp banned.