In the US we supposedly have a law that everything needs to be "accessible." That can be interpreted many different ways.
I don't know about Australia. Call ahead and ask about the facility where your imaging will be done. But you won't be the first person using a wheelchair who's ever gone there. And they won't want you to fall!
An MRV will be done on the same equipment as an MRI -- it's just going to be different pictures.
Anytime I go for an MRI, I have to leave my lovely chair outside the MRI room and transfer to a yucky hospital chair that won't get sucked into the MRI magnet. Then you transfer onto the MRI bed.
One detail is that you will usually get an IV ahead of time so you can get gadolinium contrast during the procedure. Ask them to place it so it won't interfere with you ability to push yourself -- the first time I didn't know about this and I ended up with an IV in a place that made it impossible for me to be independent.