I personally have thousands of Twitter accounts I control just for fun; I mostly use them for pranks, though in aggregate there are a few million followers between them (not sure how many duplicates there are, or, ironically, how many of their followers are bots). You can even buy software to create and manage Twitter accounts pretty easily in blackhat forums.

For mine, I scraped a bunch of Instagram pictures for photos, auto-generated a bunch of bios using a few basic parameters, e.g. "Beer lover, proud parent." Names were easy - the most popular first & last names from census records, mix and match. Grab a few lat/longs and convert them to the biggest US cities and you have a location, find some data source to tweet from (breaking news is easiest) and you have a fully automated, human-like Twitter account. For bonus points, Pick a random color toward the low ends of the hexadecimal range ( rand(a..c)++rand(0..f)++rand(a..c)++rand(0..f)++rand(a..c)++rand(0..f) works fine) and you even look like your page is personalized down to the color.

Start following random people and 10% follow back (even more if you follow people who are tweeting about similar keywords as you - kindred spirits I guess).

The only tricky part is making sure you don't cross lines with your IPs. You could buy/rent them privately, but you really only want to keep a few accounts (3-5) to each IP, so that gets expensive ($.75/IP/month) when you don't have a really good reason to use your accounts. You can scrape free listings for them, but those are nasty, slow, and can cause bans if Twitter decides to take down a whole range or if you are forced to switch IPs too quickly.

Device type, browser, etc. is easy to spoof.

Should you decide to, it's also really easy to change name, username, and profile picture of an account in the future. So if I wanted a few thousand Trump-supporting (or Trump-hating) sock puppets I could have them today.

If you don't want to buy/create/manage Twitter accounts yourself you can get access to what's called a "panel." A panel is basically an automated, coin-operated network of fake accounts that you can control at wholesale prices. Want 5,000 followers? Plug $1/1,000 followers into the panel, supply the username, and you'll have them in a couple of minutes. Or resell 5,000 followers for $25 and pocket the $20 difference. For example of a panel, see this ad on blackhatworld: https://www.blackhatworld.com/seo/the-biggest-smm-panel-yout.... Nothing special about this one, just the first I found when I googled. They're a dime a dozen.

I'm certain there are millions of fake accounts for every service imaginable.