I'm not,by any definition, an NFA expert. My "Class 3" experience is limited to Military Service,Law Enforcement Duty,& friends' toys.
However,I am one Paranoid S.O.B.!
You stated your job could suffer substantial financial losses if you are absent,&I believe you; however,(& I've no clue where you live), have you considered taking a weekend trip? I realize it could be inconvenient& may require you to arrange for the dealer to meet during non standard hours (may cost?) but would allow minimal financial hardship for your company. Otherwise, maybe try for the Thanksgiving period? Airfare will be more expensive & road traffic will be heavy, but it may be an option.
Finally,the AC556 uses the same mags as the Mini14.
I know because a Class 3 friend has an AC,& I had a Mini,& we bought bulk mags& split them.
Best of luck,