Welcome to the Bunnings Workshop community @sanzida. It's splendid to have you join us, and many thanks for your question about custom sized mirrors.
One of our suppliers, Bradley Australia, can create any size mirror you need. You'll need to speak with one of our helpful team members at your local store's Special Orders desk. They can be contacted by phone if you are unable to head into a store. They'll take the size details for your custom mirror order and place it with the supplier.
Please let me know if you need any assistance with the ordering process.