Hi Nancy - I've a couple of suggestions that are hardware-related, though not specifically the niche business of cast-brass furniture ornamentation.
I've had difficulty in the past finding iron screws that have at least an authentic look, if not authentic materials (wrought iron). What I've turned to is removing that nasty zinc coating from straight-slot tapered wood screws, but the end result is still not really satisfactory. In looking at period pieces, I've noticed that the iron screws used for H&L hinges, chest lifts and the like are slightly domed. Other than scavenging them from antiques (not something I care to do - I'd rather see an antique repaired and refurbished than gutted for parts), there are no good sources for these that I've found.
Another potential opportunity is finding smaller chest strap hinges that would be appropriate for children's and miniature chests (at least miniature by the 18th century's standards - not the 1/12 scale that most modern miniaturists build to). Horton and a few other sources sells hand-wrought hinges that have the 90 degree bend required to properly position the hinge, but to my knowledge, they're all in the 7" - 13" range.
Finally, to my knowledge there's no good source for miniature hardware on the scale of doll-house furniture. One can buy very cheaply made "chippendale" brasses that are apparently all made by one factory in Asia, but there is no style selection, and the few that I've ordered are not well made.
Clearly, these are niches that don't have a huge market, but they're unfilled needs, at least as nearly as I can determine. There might be an opportunity there if you can work some of your contacts to find someone to make these things. I've considered it myself, but setting up a brass foundry is not exactly my interest nor expertise.