The reason the grading companies were able to get Ebay to allow only coins graded by certain companies is because they organized and approached Ebay with a plan, rather than sending messages every day identifying specific listings with which they had a problem.

You have a club that can speak with an authoritative voice, and it is associated with the ultimate coin club in the USA, the ANA. Unfortunately, you lack ownership of the designs (intellectual property rights) or protective legislation (such as the Hobby Protection Act).
You need to work as an organization, determine how the ANA and other organizations have worked with Ebay, and develop a plan in advance so Ebay wants to listen to you. When they receive a complaint about a listing, Ebay needs to know it is coming from a group with which they have established a reliable relationship - and not (as typically occurs) the grumblings of a potential seller who wishes to suppress a competitor. They simply lack the resources to investigate every claim from unknown persons about listings - but they listen to the grading groups, law enforcement, etc. The key is to place yourselves in that higher echelon.