I think you’ll have to contact Aquila (the U.S. division) directly and ask them what they need to know in order to supply you. I could not find anything on their site, which doesn’t mean it doesn’t exist.
What I know about them comes mainly from banjo players (yes, there are nylon- or gut-strung banjos). There are two basic Nylgut sets for banjo, for minstrel (a fourth low) and modern pitch. Nearly everybody raves about them but says they take a good long time to stop stretching and settle in. I would expect the same to be true of Nylgut strings for harp.