Where can I get a replacement pendulum that is the right weight and length?

I have a 1974 Hamilton "Paddington" 31 day wall clock, for which we have lost the pendulum. I took a flier and bought a random one for it, but it is apparently the wrong weight or the shaft is the wrong length, or both. So, it will not run. The movement is Japanese and it has no jewels nor any model number or serial number on the back plate. The wooden case is approx. 8" by 8" with wooden scroll work both on top and below. HELP~~