You might want to begin by trying to find the value and history in Pierce:
https://www.searchppa.com/product/one-day-membership/

It's hard to sell old stuff these days. Pianos especially, because they're big, expensive and they don't always age well. But worst of all, old pianos with ivory keys pose serious legal hurdles you need to know about. If the keys are ivory, you'll have to be able to prove that it was manufactured prior to 1975 and supply the appropriate documentation to the purchaser. If the ivory was ever repaired, there may be no way to transfer ownership legally, because you would need to document the repair materials. It's illegal on a federal level to transfer ownership or move it across state lines without proper documentation, and some states have even tougher regs. An undocumented piano can be seized by state authorities or US Fish & Wildlife.

Ivory Update