what cdi unit do i need to bypass the old immobilser?

I have an R Reg speedfight 100. Havent used it for a long time but as summer is coming i would like to get back on it. The bike will start and run but it wont rev out, the garage says that the cdi unit might be the problem. I have lost the old red key for the imobilser is this a problem. I understand you can buy a new cdi unit which bypasses the old imobilser. Can anyone help? Where may i purchase one of these units. Is the cdi unit the problem.

Cheers Tom