American Amazon is full of metric magnets.

You can buy alot very cheap.

150 5x1mm for $9.50

200 for $7.50

I'm not aware of a similar product for Index, but you could always increase the distance between the HMD and the gasket with magnets (5x1mm neodymium, like these ones). That only increases the clearance, but should make it less probable to damage either the glasses or the HMD.