Hi shuswapkev,
Regarding the spares service you mention, this is the one run by The London Douglas MotorCycle Club for use by members sited all over the world,
The Club does try to carry important spares for as wide a range of models as possible. Particularly those which wear out or are often missing or unusable when bikes are found for restoration. Sadly we cannot cater for all requests!
To use this service you do need to belong to The Club, details of membership and how to apply can be found on the Club site douglasmcc.co.uk the cost is at the moment only £18-00 a year which covers a bimonthly magazine, information like the machine register (about to be circulated at the end of this month) and helps finance the spares service as well as the day to day running costs of the Club. So not expensive!!
Having recently gone through a major reorganisation the stock list is not yet published, however an email to the "spares man" will result in a rapid reply! The drive sprocket of which you ask may well be available.
Dave