how do you make a repeating crossbow or Chu-ko-nu?

Answer 1

Like james says it will be a great project,
Try looking up medievle warfair as well as estern warfair.

Answer 2

Such weapons have appeared on the History Channel and Discovery channel shows as modern-made, fully functioning models. Perhaps if you were to email them, they could put you in contact with the owners/builders of these weapons, who surely have blueprints from such an auspicious project. I wish I could be of more help. Sorry.