Mylar is a brand name used by the DuPont corporation to identify thin polyester plastic films that it makes. Actually, DuPont and a Japanese company have created a joint company called DuPont Teijin Films to handle the polyester film business.
It also appears that many large companies in different parts of the world produce similar products. It also appears that some companies may buy the polyester film from companies such as DuPont and then add the aluminum coating themselves, before distributing to consumers. In other words, there may be dozens, scores or hundreds of companies that sell polyester films with aluminum coating. This may make it very impractical to trace a supplier for you in Port Harcourt through the manufacturers, which is what I tried to do in my email to DuPont Teijin.