Given you are still acting on non-Twitter submissions it would be nice if this option could be made more explicit on the logo submission screen.
For example, the existing logo submission page could have the existing Twitter option but perhaps underneath it could also have a “Retailer does not have Twitter account” link. This could then redirect to another page which requests Facebook or Instagram or generic URL. That page could contain the message that non-Twitter submissions are manually reviewed and will take time to get added.