I've got some ivory pieces I've come across thrift stores. These pieces have no date records or any other Metadata that would verify the origins of the pieces.
Yeah, call U.S. Customs. Years ago ( late 1990's) I had a couple of Colt SSA's and wanted a set of ivory grips for them. Colt informed me that they couldn't get ivory anymore, but did have some and that a pair of grips would cost $450. I passed and I don't know though about buying or selling. Customs will let you know...