Don’t buy them, ever. What you get then is a bunch of followers but no engagement. It’s a vanity metric and it might make you look good temporarily, but it adds no value in the long run (and may even get your account banned).
You want to add social media followers slowly, organically. You want engaged people who comment on your photos and share your posts. Do this by posting regularly, keeping your content awesome, and engaging on and off your page. Be ensure to ask people to follow you at the end of blog articles or in your emails.