I definitely saw people with oxygen tanks but not sure if you can get them there
I'm almost positive you can take in your own, not sure that they supply tanks.
Yes you can bring your tank. No they don't have any tanks to rent.
You can bring your own, though some rides, such as roller-coasters, have restrictions which won't allow you to bring an oxygen bottle on with you. Disney does not provide it rent oxygen, but there are a number of 3rd party providers who cater to park visitors and will rent you a system for your visit. Just Google "Walt Disney World oxygen tank" and you'll get plenty of hits to start with.
Thanks! Your answer is awaiting moderation.