The numbers are higher than you'd expect. The trade in illegal (and so high rarity and limited access) goods is ongoing and flourishing via the use of third party intermediaries like free port systems [1] as well as networks of morally grey curatorial and preservation staff. Several notable archaeological "missing links" of the past few years came from said staff mediating access to private collections of undescribed provenance.

[1] https://www.theartnewspaper.com/2015/07/01/experts-identify-...