Hi @AndrewLynch,
Welcome to the Bunnings Workshop community, it is wonderful to have you with us.
Unfortunately, there is no suitable method for mounting a dryer to plasterboard, regardless of the strength of the anchors used. The issue isn't so much with the weight, but with the vibration of the machine. Plasterboard is a thin material that is essentially compressed gypsum between layers of paper. With the weight and consistent vibration of the machine, the plasterboard will get damaged, and eventually, the plasterboard will fail, causing the fixings to pull out and the dryer to fall off the wall.
The only solution I could recommend is mounting them to the studs. You can use a studfinder to help locate them. Check out How to use a stud finder for some guidance.
Let me know if you have any further questions, I am happy to assist further if required.
Jacob
