Welcome to disABILITIES. Glad to hear you have found it helpful already.
I don't have any personal experience (hopefully, you will get a reply from someone who does), but I can give some advice.
First, I'd suggest you contact your home supplier and tell them your plans (if you haven't already). If you are lucky, they will be part of a national company that has a branch near Orlando. Or they may have worked with vactioners to Orlando in the past and have suggestions/a place they have dealt with. At any rate, they should be helpful in making sure that you get what you have at home.
These 2 medical equipment companies that DIS posters use for wheelchair/
ecv rentals also list respiratory equipment and oxygen:
Care Medical:
http://www.caremedicalequipment.com/
Colonial Medical
http://www.colonialmed.com/about_cms.html
If you are staying on site, you can also work with WDW RESORTS/SPECIAL RESERVATIONS
(407) 939-7807 [voice]
(407) 939-7670 [TTY]
They are the department at WDW that deals with getting special needs and equipment requests for resort guests.
Whatever company you use, they will let you know what they need from your doctor, in terms of prescriptions and information.
Good luck and please come back and post about your experience.