I got all my Carradice stuff from Rivendell, www.rivbike.com. They used to have a huge selection and could order almost anything. Not sure they still do, because they're carrying their own stuff now, but they had a really cool adapter with a quick release so you could unhook the bag and carry it with you.
Not cheap, as you already know if you're using Carradice. If you don't see what you want on the Web site, give them a call--they have all kinds of stuff in small quantities they don't always post.

EDIT: Took a quick look and found this: http://www.rivbike.com/products/list...product=20-109
But, holy crap, 86 bucks?