Why not set this up as a table inside of Filemaker? That gives you a lot more options for how to do what you want.
Could you please give me the details on the programming format, etc.
I'm not sure what you are asking for here...
There are a number of threads here that discuss inventory management and others describe invoicing system. You can click the Advanced link to research these if you are interested.
What exactly do you want to set up?
I've suggested moving the data (or form) from Word to filemaker because this is a database process that you appear to need. Let database system do database things and word processor do word processing tasks and generally speaking, the work gets easier.
As I enter new clients with the parameters of the item(s) that they want to purchase
using separate fields, I want to be able to automatically find out what items clients are
waiting for as I enter the new inventory when it comes in.
That's a typical invoice and inventory management system.
Here's a link to logging inventory changes so as to compute available inventory:
and here's link to a thread that includes a demo file that's worth looking over to see if it can work for you: