1. Open gfx\everything within the NDF_Win.dat
2. Search "TModernWarfareSupplyDescriptor", which should be number 118 down the list
You now have a list of all the different kinds of supply. One of them references FOB supply.
3. Open number 42609 from the center column- this is FOB supply (you can tell because of its "SupplyCapacity")
4. Edit to your liking and save. As you can see, I have mine set as 40,000.
Note that this is only the supply, not the FOB itself. The FOB units are located in "82 : TUniteDescriptor", should you ever need to know.