Hi,
I had a similar problem obtaining replacement rubber drive belts for the encoders on my Tak EM10 USD mount.
According to Gary at Wildcard Innovations, the Takahashi encoder kits were custom-made by JMI in Colorado. Unfortunately, JMI divested themselves of much of their business and sold some of their IP to Farpoint / Optical Structures, Inc (OSI) in California. Farpoint (
https://farpointastro.com/) may be able to help you out.
Best,
Kevin