Fancy goldfish need a minimum of 15 gallons each with VERY good filtration - Commons need a pond. Even if you gave away full 20g setups with each fish (unrealistic, of course) the chances of the recipient actually caring enough to properly take care of the fish are low. Most of us who remember this game from when we were kids probably also remember that the poor fish didn't last very long once we got them home.
I think your idea is a very poor one - any pet, including fish, should be a well thought out purchase and not the end result of someone playing a game on a whim. The chances of any of the fish being well taken care of are slim to none.
I personally wouldn't be selling small bowls and tanks at this kind of event either. People see these items and assume they are suitable for all fish and truth is they are not suitable for much. Nano tanks can be difficult to maintain and I can see plenty of disasters with these set ups.
Your question "Can one gold fish live in a one gallon bowl with 20% water changes every week? Will it be okay without an airstone?" leads me to believe that you really don't know that much about fishkeeping and need to do ALOT of research if you want to be a responsible business owner.
Quite the opposite actually……
I’ve never bothered with a fish in a bowl much less a gold fish. (Unless I got it at a fair) it was always a full tank or nothing. I’ve done everything from planted tanks to reef tanks to natural biotopes and dabbled in some breeding and coral fragging.
I used to play this game as a kid, it was my favorite. Many times it caused me to come back to the hobby or to get a larger tank. In the end all the goldfish died but the enjoyment I had made them much more then a simple feeder fish. They were spot, blacky, knight, goldy, etc, etc, etc. Now to me if I had a choice a bad life with love or dinner guess what I would pick?
This game has people all up in arms; I think I’m going to go through with it though. In the end its permitted by law with the permits and I like the feeling of the old days the game can add to an event. Sorry.
As far as responsible goes…..
I’m trying to equip each person as best as I can and I want them to leave with the information necessary to be responsible pet owners. Let’s not forget a goldfish from the fair was a lot more than a fish in a bowl for many children it was a first pet an opportunity to get a little responsibility at very little cost. I’m also trying to ask for input on how to do this the best way, I can take constructive criticism but lets concentrate on helping the fish if this situation is inevitable.