You're doing a lot of detective work over this, mate. It seems a shame that your taxes aren't being put to work in having the authorities looking into it all for you at this point. You have a few pieces of evidence already.
If you decide not to involve the cops, you could always consider going private. Those guys have access to various databases and have friends in all kinds of records offices that could unearth whatever you need to resolve this or at least expose any illegal activity the London Coin Company / Numismatic Worldwide might be engaged in.
Not cheap, but the satisfaction could be priceless. And if it does unearth something criminal you have every chance of recovering your funds or the coin.
I think this runs deep, they must have cover accounts on eBay
hes doing a good job i think its just a matter of time