I ordered an upper and lower from them no problems.
But when I tried to order magazines they are back ordered.
Is there an aftermarket magazine that will work?

Fn-FAL surplus magazines used to be their supply.

FN-FAL-type detachable box, compatible with both inch and metric pattern FN-FAL magazines

A FAL for .40?

The metal surplus work better than the factory plastic.

There's a surplus metal mag that'll fit the Rock River .40 cal?

Sorry - I read it on the smart phone - read it as -10 on the little @ss screen.

No - the .40 mags are Rock River only as far as I have found.