Sorting of drop down menus.

Hi,
I have a form with a field that is linked to a table/ drop down menu of around 3000 suppliers (which I have uploaded).
New suppliers are added to the table almost every day though a different form.
How do I get the drop down menu to add the new suppliers in alphabetical order?
At the moment the list comprises of the original 3000 suppliers that I uploaded in alphabetical order, however any new ones added are only added to the bottom of the drop down box which makes it difficult to find as there are so many.
I hope that make sense?

Jamie