In the possible arena of post-1500 (the 16th C. and later), I would look to a more-direct connection to China and Chinese beads, from across the pacific. Possibly entering the NW via the Aleutian Islands. Although they are not precisely dated, some Aleut ornaments include what might be early export beads from China.

Of course, one could postulate that these are late enough that they got to the Aleuts from the N.A. interior, via conventional trade relations that are recognized.