I've been accused of being a backward boy. I grew up with great insecurity because I never knew where or when my next box of ammo would arrive, if ever. Back then I wasn't talking about multiple calibers, we were talking 22 rimfire. Having 2 full boxes was riches beyond my fondest dreams. Once my uncle guessed my problem (he had girls) and gave me not 2 boxes, but two bricks of ammo. I couldn't sleep at night for a month. And I violated one of dad's rules about storing guns and ammo out of sight. He gave me a pass, understanding how comforting it was to me to be able to look at it. There was a light on a pole out front and down a little. I stacked them on top of each other, right where that light shone in. That way I could wake up and see them. Made me feel all warm and fuzzy. I felt better then than I can even describe. I had a similar but lesser feeling when I put a semi auto on the dresser and the Tritium night sights lit up the room.
I'm sure that early upbringing was partially responsible for my adult feelings of never having enough ammo. We moved a couple of years ago, and everyone questioned my sanity. The most common thing was "why does anyone need that much ammo". Especially from my son's who had to cart it all out of the old house. They kind of got even because they gave it all back, but wouldn't help me move it into our new house. I just loaded it from the van to the back of a jeep, then drove around the house. For a while I even relaxed thinking I had enough. But now I have this question coming back that maybe I don't really have enough ammo. Once, a couple of years ago, I even sold off the ammo that I didn't have guns for any longer. But rebuying a caliber was painful, so now I've vowed to just keep it.
And a side problem of this phobia is reloading components. Someone asked recently, and I think it was my oldest son, in disgust, asking me if I had any idea how long it would take to use all of the components I already had. That was while he was carrying 2000 bullets out to the car. The discovery is related to projectiles aren't Texas cotton balls.
The simple fact seems to be that its a harmless hobby. It can get kind of expensive.
The answer to the OPs question is ammo is where you find it. I'm convinced that It takes years of trying to ever obtain and keep enough ammo. I know people who don't have any ammo they've had more than a year. They just shoot it up. I could never do that, so I have stuff of mixed heritage. The other people may have a better system than I have.