this type of case is called a flight case. there are companies that make them for you or you can buy the parts and make your own. You can find them second hand on ebay or any place that sells second hand items.
While it does look like a Anvil case, the locks look different than anything they used. Could be that they took an Anvil case and swapped out the locks.
Would defo think its from a company that specializes in cases for music items.
In the Imdb link try contacting the production companys one by one from the top, i searched GK films because they were at the top and there is an email for contact,, they can only say no.