Hello, I’m Nathan, and I’ll be assisting you today. My livelihood depends on your positive feedback, so your satisfaction is my highest priority.
Sorry to hear you’re having trouble.
Unfortunately, this part is simply not available. This is typical for this brand/product however. The rocketfish products are proprietary and not well supported. Even for a current model, they do not make parts available. If you were to have a problem under warranty, they'd replace the entire unit. Beyond that, and especially for an older (2009 model), there is no support for them.
You could try replacing the ear cup with a comparable part from another manufacturer of similar size, but the fit would not be perfect, and it would have to be attached with adhesive (such as silicone caulking) as the mount points won't align properly: http://amzn.to/1KjXMjx
Based on the age of the system though, it is already past its expected service life, and you could expect a failure of the internal battery or transmitter base at any point now. With that in mind, it may make more sense to invest in a new system, getting an all new product with a fresh warranty and the ability to buy future parts when needed. If you'd prefer that route, I can recommend some options for you.
Best regards, ***** ***** for the news,