Jeffries and Sabre do them but they are over £35 each, I got a cheap shires one from my local tack shop to try and whan I knew my mare liked it I bought a nice english leather one from here www.tackshop.com - cant remember the name of the makers but it was £22 and is nice soft english leather, I ended up buying a full bridle to go with it.... they are not listed on the website but they do mail order so if you call them I'm sure they would help....
Thats the one I had originally - seemed ok quality until the leather came off the metal ring and the ring dug into my horses face... <rolls eyes>
try old dairy saddlery. look under bridles and scroll down, they are selling all types of nosebands separately including a drop and at the moment offering 20% off the list price.