You can manage your Vendors by Inventory Location and add account numbers if needed.
To do so you can go to:
Management > Corporate Setup > Inventory Locations
Choose an Inventory Location and click the Vendor Accounts tab at the top.
Enter the following information:
Select Vendor: Use the dropdown to choose one of your vendors. You can only associate existing vendors with inventory locations. To add vendors to the system, see the article Add a Vendor.
Account Number : Enter the account number for the vendor if not autofilled. This vendor account number will appear on Purchase Orders created with this Inventory Location.
To make changes to a vendor, you have to delete them from the Inventory Location. Click the trashcan icon to the far right. You can then add the vendor with the needed information.