I got my belt out of an old printer I’d broken up, being a large loop of the stuff I just cut it to the length I wanted then re-joined the ends using Araldite and heat shrink tube. I should think these guys will have what you are looking for though
An update:- A couple of findings,the motor and belts work as planned. No need for gear wheels on neither the collimator nor the micrometer spindle. No fear of belt slipping off the collimator due to lip on the end and both focus motors and micrometer have rubber tap washers on the ends to stop belt slipping off. I am planning on changing the Skywatcher focus motor as it is a bit on the bulky side and now the Lhires will not go back into its supplied case, because of this I am looking at purchasing a much smaller JMI focus motor so as that the box covering the motor now can be done away with. I did state in my last message that there was some shift when operating the focus motor but realised afterwards that there is the same amount of shift when operated manually and also the lock screws need to be adjusted just loose enough to allow the collimator to turn but enough pressure to stop it tilting toward the motor. Same again with the belt, there is hardly any pressure against the collimator and motor, just enough to allow belt to keep contact without slipping .