Welcome to the Bunnings Workshop community @iankelly. It's great to have you join us, and many thanks for your question about asbestos sealing paint.
Was there a particular product you had in mind, as I am unaware of any products specifically designed for that purpose? We carry standard exterior paints which according to documents from NSW Gov should be suitable: "Asbestos sheeting (such as fibro) and corrugated asbestos (walls, fences and roofing) can be sealed with good quality paint." However, in order to paint a roof you would need to prepare the surface thoroughly so the paint can sufficiently bond to it.
One litre of paint typically covers eight square meters with two coats. So for 140sqm, you'd need approximately 18 litres. Two ten-litre containers would likely do the job for you depending on the sheeting porosity.
It's advised that when the asbestos can be removed it should be. So, I'd recommend you seek professional assistance with your project and if the sheeting can't be removed, seal it with products designed for that purpose.