Staff cannot be trusted with access to department budgets, that is why only Heads have access to them. There is almost ALWAYS a Head of Staff on, and any head of staff can, if asked and have the time, get you an account number to charge an account.
I seriously doubt you will run out of supplies this quickly. If you are, then - charge with an EFTPOS to your personal account, keep track of how much you've made via it, and then use that to buy cargo supplies.
Phoron is worth 100 credits per crystal sheet.