I have made a few springs for my Merkel's OU 201, the spring is similar to the Miroku blade spring. The steel is critical as the hardening may differ.

What I did was simply to follow the description and then, after hardening and polishing, I heated the finished spring with with the small gas burner to lightly yellow. You may need to experiment with this but I managed to make a spring within two hours.

I had to buy 5 meters of 5mmx25mm steel, so I will have enugh steel for my lifetime. The price was 11€ for the steel. Since then I also made a broken ejecter for my FN Browning Game Gun from the same steel.

regards,