You might be able to take thread from another part of the garment . . . depending on how it's made, and how fine the fibers are--whether they're of a size you can work with. Whenever I take a sweater in to the Alterations and Reweaving Center, the lady looks for ends of thread that have been tucked into the seams, because that's what she'll use to fix a small hole or mend a tear. If it's very fine thread, it might be challenging. This lady effectively puts the garment under a microscope so she can see what she's doing!