Welcome to disABILITIES.
Here are links to the companies that DIS posters have reported good experiences with:
Care Medical:
http://www.caremedicalequipment.com/
Walker Mobility:
1-888-726-6837
www.walkermobility.com
RANDY'S Mobility is in Kissimmee 407-892-4777
http://randysmobility.com/
Colonial Medical
http://www.colonialmed.com/about_cms.html
(One warning: I am using my laptop, which I haven't used for a while, so the links may be old. The companies are all all the same though)
I don't have a lot to add to Nanajo's bus instructions. Some places (like the parks) do have a spot that is marked for people with wheelchairs/
ecvs to wait - you will see a wheelchair symbol that tells you where to go. For the other stops, just park close to where the bus's back door will be when it stops (easier than it sounds).
Almost all the buses have either a wheelchair lift or ramp that comes out of the back door. Make sure to practice backing up since you will need that skill to get on the bus. If your party is 6 or less (5 plus the person with the wheelchair or
ecv), you can stay together for the bus. If some wait by the backdoor and some wait in the line, you risk not all getting on the same bus if it's busy.
For waiting in lines in the parks, most waiting lines have been made wheelchair accessible, so in most places, your whole party will wait in the same place as everyone else. In most cases, your whole party (6 or less) will be able to stay together. There are places where this is not possible because of the amount of space for waiting or places designated for guests traveling with wheelchairs; if so, the CM will instruct you on the number allowed.
If you go to Guest Services in any of the parks, you can get a Guidebook for Guest with Disabilities for that park. It's kind of basic information, but does give info on where the accessible entrnace is (in most cases, the Guidebook says "Proceed to the regular queue." Just having an ecv or wheelchair allows you to use the wheelchair entrances where they do exist -no need for anything else. The GAC that was mentioned stands for Guest Assistance Card. It's basically a way for CMs to be able to quickly tell what sorts of assistance someone with invisible disabilities needs. Examples would be allowing a stroller to be used the same as a wheelchair for someone with a child with special needs that make a stroller in lines a need. Most of the lines are covered (some are even air conditioned. Using fastpass (which is available to everyone) generally makes your wait in line 10 minutes or less and the entire wait is usually in a covered or inside area.