wheat noodles (yakisoba/chuka soba)
Yellowish wheat noodles made with alkaline water, the same kind used for ramen: springy and firm to the bite.
They are sold fresh, pre-steamed or dried in Asian grocery stores, often in the chilled section, and dried ones sometimes turn up in well-stocked supermarkets. The alkaline water in the dough is what matters, since it gives the noodles their springy firmness, so they hold together when stir-fried.
Substitute:
Dried ramen noodles or instant noodles without the seasoning packet come closest. At a pinch, boil spaghetti in water with a little baking soda, which makes them yellower and springier, though still a little less bouncy.