I assume you are asking about Atlanta, Georgia, USA. I have not been there for a couple decades. But I did a few google searches.
Some larger communties in USA have bicycle charities where they try to help less-fortunate kids learn skills and maybe retail experience. My google search turned this one up. They might accept donated bikes, fix them up and re-sell them. Such bike charities often have limited selection but if you are looking for a bike for a few weeks, I suspect you can be less selective.
http://southatlantabikeshop.org/about/Some communities in USA have a bike coop where people can go and borrow tools, etc., to work on their bikes. I do not think that any bikes are sold at this one, but it might be a good point of contact.
http://sopobikes.org/welcome-to-sopo/Or, bring a foldup bike in your luggage. If it was me going there, I would bring my S&S coupled bike (a Thorn). I have no idea what the potential for bike theft is, but larger communities in USA can have a theft problem. So, you would want a very good lock.
Where to stay? I have no idea.
