How can I create a unique list of data across columns containing text "Retailer Name"?

I have certain data where I want the unique Retailer name across multiple sheets and multiple columns containing "Retailer Name" as the heading. I've shared the editable gsheet link, kindly help!

https://docs.google.com/spreadsheets/d/1RM21N_w7mWTltMQi5Iq-p8iBaqJwegj94NwZVxfy5ng/edit#gid=0