It seems at first that accumulating bottles is difficult but if you mention around to people that you brew and need crown bottles they will start showing up. There's also craigslist, and freecycle.org, hooking up with other homebrewers, recycling centers. Asking at beerstores that have a good selection of beer for their returnables. Some stores will let you have their empties for the price of the deposit. And some bars will give you all you can haul out if you ask.
Also if you want to bottle in champagne bottles, go to a hall that does weddings, heck even a moose or vfw hall, you might just have to dumpster dive at worst, or just pick cases of empty asti bottles by the back door.
It seems daunting but you'll get plenty really fast. But in reality when you annouce you are homerbewing, they do come flying at you. I even had my building super years ago just use his key and leave me some on the dinning room table. He knew he'd get beer from me on a regular basis, especially if he was gonna do some work in my place.