I've noticed a lot of messages on this forum (and others) from people unable to obtain Cox .049 engine spares and fittings, go on to eBay and search the online shops for "XENALOOK" they carry a large range of new Cox spares.
They are a Canadian company but ship worldwide, I have had excellent service from them, they don't have every spare obviously, but their stock varies regularly and the odds are that sooner or later you will find what you need. Or contact them and ask if they have what you are looking for.