Hey Jeffrey, for a temporary solution a standard 3mm cord should work like the Mammut Hammer Cord. For a longer term solution you should reach out to SCARPA as you'll want a spectra cord that doesn't stretch.
It looks like you're out of Alien RS 30.0 cords -- would either the 30.0 of the other boots' cords, or the RS cord for a smaller size work? Or should I wait for the proper ones to be in stock?
Just measured with Alien RS and you can use the "Alien Dyneema Cord 28.0-30.0" which will work with the RS. You might want to tie an overhand knot above the cam mechanism on the RS just to prevent it from tearing away the sheath in the future...that is what I do. Hope this helps.