Oh for goodness sake! Once again I can easily see where this whole discussion is going to do nothing but confuse the OP as to what to do.
Regardless of how you feel about alkaline powder, baking powder, & baking soda - NONE of these items are ingredients for homemade ramen noodles. Don't believe me? Do a websearch like I just did for "homemade ramen noodles". Not an iota of alkaline powder, baking powder, or baking soda in sight.
Again dear original poster - don't worry about a substitute; just leave the "alkaline powder" out.