To be honest, I've never seen a man wear a shawl in Mauritius. I might be wrong or you might have referred to a different cloth and quoted something else. I'm thinking the first places to go to are maybe where they sell Indian clothes (saris and churidars) where they might have a man's department selling shawls.
You want to be in Port-Louis. Toorabally, Tulsidas e.t.c are quite renowned for their clothing.