I’d say to cut two slabs of some kind of hard wood and use that as your practice.
Antler material cuts and sands fairly easily, but you have to be aware of the grain direction and thickness to make them look just right. The nice thing about antler and bone is it’s cheap and readily available.
Here’s grips I made for a ahh umm...Ruger for a local Wyoming rancher with a moose Antler his son found. I think from this photo you can see how the antler cut was made.