This was posted by the Parkinson's Disease Foundation on their Facebook page:

People have been calling our Helpline reporting being impacted by a shortage of Sinemet CR, the extended release formulation of carbidopa and levodopa. We’ve been in touch with the manufacturers who acknowledged the shortage and anticipate resupply by late October. People who are impacted by this shortage should talk to their neurologists about three potential options: (1) your pharmacy may have Sinemet CR pills in different dosages, and you may be able to take a different combination of pills; (2) your neurologist may be able to substitute immediate release Sinemet, or (3) your neurologist might recommend a new extended release formulation, Rytary. Please call our Helpline, 1-800-4PD-INFO (473-4636) for assistance.