Sorting with drop boxes

See attached example if needed.

I've set up a great big thingy, much like the example given, here's the problem -

Adding new items to the list, and then sorting them, I've found that the drop down boxes which I was oh-so-happy to utilize... don't move with their relative rows when the item name or department is sorted. IE. The option to select Supplier 3 for Thing 4, stays where it is if you sort by department, giving incorrect options. Any suggestions on how to sort this while moving them, or on an alternative menu box system which would sort?

Thanks!