Request it at checkin - or even call beforehand. This way, the wheelchair should wait for you outside of the aircraft as soon as the doors open. It would not hurt to reverify with the GA in TPA of course
Asking the GA may work but it will work only if there are non-reserved wheelchairs and you don't want to gamble on that in a hub.
If a mobile cart will be enough, it is a bit easier but I would still call beforehand and warn them.