Sort With Data Validation

I've found that sorting a column next to one which has drop down boxes set up in it, does not take the options for the drop down boxes (data validation ) with them when being re-arranged. Is there a way to make this possible, or an alternative format I should be using? see example:

If item 4 is the only one available from supplier 3, (As shown by the drop down box options) how do I sort by say, department, and still have the correct options on hand? Sorting by department, the items move, but the data validation info stays where it is, leaving the supplier 3 option for item 1, which is not correct.