List problem

I have a combo box that will be populated in a FlexiGrid when a form loads up. However on the program I am making, the item selected from the drop down box can only be used once. So I need to somehow update the list as one item is selected, removing it from the list so that then populates the next combo box without the selected items in it to prevent users from selecting the same item twice.

So for example the following items are populated in the combo box from a Stored Procedure from a SQL Database:
'Controller'
'Book'
'Tv'

So say if Row 1 the user has selected from the combo box a 'Controller', the list then removes this item from it and then whatever is left gets populated in the list again.

I have tried a for each loop that ran through the rows in the flexigrid but I just kept hitting a brick wall and getting nowhere.

It seems pretty confusing. It's difficult to explain haha.

But thanks for any possible help!