I don't think it's possible to buy exactly the ones worn by the actors, but try to find out in the internet. I've seen an online shop selling stuff from Lord of the Rings movies (on the official LotR site). Who knows?
Maybe you could ask in some theatres near your place. The costumes there might be similar and your could find out how theatres get such things. Maybe there's a way for a private person ( not an institution like theatre) to buy or somehow get a costume?
Good luck in seeking