If you see one on eBay, just post it in the "Authenticate this" thread at the top. There are genuine Mulberrys on eBay but also fakes.
The couturedemode website looks like it sells fakes because you can only buy LV online at eLuxury. So if those are fake the other bags might/could be fake too.
I bought my bag at the Mulberry store close to where I live, at retail price. Saved up for it. Not cheap, but I see it as a good investment that will last me many years. And I'm 100% sure it's genuine.
I hope you'll find the bag you're looking for!