If the people making purchases aren't trained on the Purchasing procedure, that could be a decent-sized gap.
If they're trained on it an ignoring it, that could be more of a management issue. Their boss might need to remind them to use the company credit card correctly. They might not be the correct person to have a company credit card.
Thinking a little further outside the box, how hard is it to update the approved supplier list? If it takes two weeks to update the ASL, but the company is going to lose internet access in less than two weeks, someone might ask for forgiveness rather than permission.