How to make a dotty halftone gradient effect?

[James Loudon]

So I am working on designing some tattoos that I want to be done using a dotwork fill, like this:
I cannot find any way to get near this sort of fill! Maybe someone has designed a plugin, or let me know if you have other ideas. At present all I can think is to manually make a fill with dots and ink on paper, scan it and use as a bitmap fill. It will not be the actual artwork used but needs to be close as poss, as the tattoo artist will obviously use her own skills and method.
Thanks