I just got back from my WEB Search and if you go to My Favorite WEB Search Engine, you'll get quite a few hits that include, among others, Tub and Spa and Whirlpool companies. Most of the ones I looked at install corner whirlpools! This implies you might be able to contact them about a curtain rod.
Good luck! (And it seems that a visit to some Bed & Bath places might work along with a few visits to Tub & Spa Retailers.)