CanadaRealEstateSigns.com produces magnets in .020 and .030 thicknesses. They can be custom cut to any size. Below are some typical sizes.

2 colour promotional / fridge magnets. High quality .020 magnetic vinyl
Business Card Size: 3.5"x2". Fully customizable.

Qy: 500 - $199.00

Qy: 1000 - $299.00

2 colour vehicle magnets. 12"x24" High quality .030 magnetic vinyl

Qy: 2 @ $46.00 ea.
Qy: 4 @ $42.00 ea.
Qy: 6 @ $38.00 ea.