Know anybody who won't be flying? Most engines in the .40-.50 range from various manufacturers use a similar hardened 1/4-20 nut. Maybe you could convince them to cough up the nut until you can get the replacement. I know exactly what you mean about it being the weekend and wanting to fly. I've been up until 2-3AM on Friday several times so I can have something finished in time for the field the next day.