As was already mentioned, just let the parking lot CMs (each one you come to) know that you have a mobility device that can't go on the parking lot tram.
They will either show you to a spot on the end of the row or send you to the handicapped parking lot (which they call "medical parking"). There are certain spots in the lot that you need a handicapped parking permit to use and there are others that you can park in without one. There is more information in the disABILITIES FAQs thread near the top of this board.
If you are staying on site, most people chose to take the bus to MK, even if they drive to all the other parks. The bus lets you off close to the turnstiles.