Don't know if they are still in business or still make and scrimshaw grips, but about 30 years ago I had a couple of elephant ivory sets made for Colt SAA's and a set for a Ruger Bearcat by Boone Trading Company in Washington state. They offered elephant, mammoth or imitation ivory grips, custom scrimshawed or checkered if you wanted it, and also sold legall raw blanks of all the materials as well. They already had patterns for the Colt sets I wanted (2nd Gen), but I had to send them the grip frame off the Bearcat to make those grips from. So they did do nonstandard grips then, and probably could have done the Dragoon. Might even still have one of their old catalogs in storage - kept because they had a lot of great pictures of scrimshaw patterns for all kinds of projects.
BTW, as touched on, not all imitation ivory material is created equal. Those worth having are pretty expensive, although still much less than the real thing. And I agree, lots of luck finding a T nut big enough to make Dragoon grips out of.
HTH