You're probably better contacting Saints direct. If you're thinking of non-match days then you can park anytime and there are plenty of disabled spaces at the stadium. However, if you are thinking of match days then the spaces have to be booked and so you'll need to contact the club direct. I don't know whether there are any spaces closer to the stadium but the ones I know about are near the multistorey car park next to the glass museum, which is less than a 10 minute walk from the stadium. Not very helpful if walking is the problem! But the walk can be done almost totally on the flat (just one kerb to bump down) and so it is possible for a wheelchair to make the trip.