Chris is a friend of mine, and knows his stuff. Also, there are harp string makers who can make up just about anything you want. Those can be expensive; $15/string, or so, but they last a long time.
I've often thought that 'Pegheds' would work well for sub-bass tuners on a nylon strung harp guitar. These look and work like friction pegs, but actually have planetary gears built in that produce a 4-1/2:1 gear ratio. I've been using them for some time, and they have worked well. They produce them in two types, made for peg boxes, such as on a lute or violin, and flat heads, as on a Flamenco guitar. They were devised by a 'cellist who got tired of dealing with the issue of friction pegs, and are virtually 'transparent' in use: neither the user nor the audience will readily see the difference, except that they work so much better and easier. They cost about the same as other good tuners.