May I ask if alcantara ear pads size are available for ATH M50?
I have checked on Shure's range and thought of asking of alternatives.
Velours should work you I guess. The DT250 pads is a popular replacement for headphones that companies don't offer first party velour pads for.
It seems to fit.
If they(1540 pads) are the same size as SRH940's pad, they will fit the M50 loosely. But they will fit.