Ivory will be all but impossible to get as it can no longer be legally sold in the U.S. (and many other parts of the world) due to recent regulations they put in place, I believe around 10 years ago or so.
However, the handles for the .32 frames really aren't that big or thick, and a lot of the companies that sell exotic knife handle materials for scales probably sell something else you could use that could approximate ivory, such as smooth bleached white bone. Pearl grip material might be possible, but it won't be cheap. Check out Jantz Knife Making Supply online. They have everything from giraffe bone, stag, regular bone, simulated ivory, etc.
Beautiful work on the boxes, very classy.