Custom/Large Poster Case. HELP PLEASE?

when the bruno mars doo wops and hooligans album came out he gave away two signed posters randomly with the album. Luckily enough i got one...and i wanna put it in a case to hang up on my wall. But its 4 feet tall. Idk the exact dimensions, but does anyone kno where i can find/buy a case 4xSomethin feet tall? Thanks in advance :)