You're already saving by using a fulfillment house in each region. You could save a little more on costs by sending the product to the 3PL already picked and packed. If your product is repacked in a mail-ready package that will save some. You could take that one further and send the picked, packed and labelled product to regional mailing houses. The post office can also sometimes help with bulk mailing projects of this nature and that would eliminate your 3PL costs entirely and also ensure you're getting the lowest shipping rates.

Also, your 3PL should be providing you with information that would allow you to track this data. Why are you not getting that information? Also, why is your current operation not scaleable, have you reached the limits of your providers? Not sure I understand that part.