I got the largest sized plain visor last weekend from supercheap.
think it's 170x150 or similar, it's a little too big on the sides but it covers the entire dash, no gaps. Cost like $10, is reflective on one side and blue on the other. Good thing is it's made from hard bubble wrap stuff, makes it a pain to store but it doesn't fall down or bend in the middle and expose bit of the interior.
It's meant to go blue side out but I found it works better silver side out.