Думаю много кто искал, теперь можно скачать без проблем и заморочек с сообщениями

MultiMerch makes it possible for other sellers to sign up and sell their products in your OpenCart store. You as the store owner can assign them to different seller groups with different commission and fee rates and manage everything through a single administration area.MultiMerch doesn’t impose any limits on numbers of sellers or products so you can have as many of them as you can get!