So from the very beginning of Avengers: Age of Ultron we see Tony Stark flying around as Iron Man, we also see the Iron Legion and an automated repair room for them. There is also "Veronica" The Hulk Buster, and a War Machine without the ugly paint job. So did I miss an "Iron Man 4" movie when he built all that stuff? Is it actually ever explained where he got his suits from, considering he blew them all up in Iron Man 3?
Given he's both a playboy billionaire, and previous movies have shown he manufactured his suits himself, I'd say it's safe to assume he fabricated them using his own resources. He came out to the public as Iron Man at the end of the first film, so he doesn't really need to be completely covert when it comes to building these things, and can easily afford his own facilities to handle the job. Given he's also a genius at robotics, it shouldn't be hard for him to build a facility to fabricate his suits using next to no human interaction as well. I believe during the first movie you see him issuing commands to Jarvis about how to paint the updated suit, after he asks Jarvis how close it is to being fully built.