When you mention a dropdown box, are you using the combobox control? If so, I would just use some vba.
However, have you tried using the Filter, which is found under Data of the Toolbar? To use it, just insert a row on your data sheet right before your first row and give each column a heading, such as Item Number and Item. Then click on cell A1 and go to Tools, Filter and choose auto filter.
Unsolved 
