I didn't get enough response to approach the manufacturer to commission a batch of M20 brake drum/ sprockets..However, it is likely he will do another batch when he perceives the overall demand to be sufficient.
For those who contacted me I'll try to find out when that might be and let you know when they become available again....Ian

email (option): ian@wright52.plus.com

Hi Ian I'm not in any hurry just let me know when he does and I will take two. thanks
gflash11@hotmail.com