Chow mein noodles are wheat-based Chinese noodles that are made with or without egg.  If you have a hard time finding them, simply replace with ramen noodles (the ones from the instant soup packets).  Egg-based noodles are generally not a good substitute as they will thicken the sauce differently and tend to have an eggy flavour. I also am not a fan of spaghetti noodles, and better to stick with ramen noodles in my opinion.