By “Retaining Ring” you must be referring to the Retainer Band as opposed to the thin silicone ring attached inner wear… yes you can get this individually on request. Send a message to the support email for the invoice.
The Corkscrew is highly adjustable to size so you should have no problem setting up the one you have to fit.
The wire thickness of the coil is the same for all the Corkscrews.
