Side note, I was in the process of applying to Sam as an accountant (Boston office). It was taking too long so I went to bed. I went back to finish my application and the job was filled. I was pissed lol
Anyway, you can get them from a ton of places like craigslist, ebay, scrap yards, breweries, etc. Some times they are really hard to find for a good price. I've been looking on and off and still can't find them. I even tried a few local breweries and still nothing.
In terms of it being illegal, don't worry about it lol When is the last time you heard of cops coming after someone that didn't return a keg. The deposit is to cover the cost of the keg. New kegs to the public cost $130+. To breweries that buy them in bulk it costs a lot less. When you buy growlers, you pay a deposit. Do you feel bad keeping those?