Refresh my memory, no sarcasm.

I don't believe ARCOS is currently set up for IA's. As a practical matter, if you don't answer your phone, it's difficult to get an IA.

Can you be assigned an IA mid rotation via ACARS, for example?

Not really necessary because the GS, and more specifically, GSWC is such a sweet deal there's apparently no limit to the amount of pilots who will pick them up. Fine by me.