My blue clickie was to the US Fish and Wildlife website, directly to the FAQ (frequently asked questions). This thread concerns "fossil" ivory, not ivory under the endangered species acts, etc., but the FAQ has information on many other aspects of collection, sale, restrictions, etc.
Canadian Inuit ivory carvings from the Inuit co-ops are given a unique number that identifies the carver and the location of the co-op, i. e. Baker Lake, etc. This protects the purchaser from cheap oriental imitations since the ID is kept on permanent file. Initial (but not subsequent) sale of quality registered carvings is through select authorized dealers. Only "fossil" ivory items may be legally shipped to the United States.