Thank you very much digitS!Just from memory:
It appears that the Makah Indians, on the northern part of the Olympic Peninsula, had this potato prior to the arrival of the Americans and the British.
The Spanish ventured north from California and established a trading outpost on the peninsula. Apparently, there is some historical and archeological evidence of that, including an indication of the growing of food crops. It would seem that they brought South American potatoes and the Makah recognized their worth.
Dahlia, you can buy seed potatoes from Irish Eyes Garden Seeds, outside of Ellensburg, Washington. I've purchased seed potatoes from them before and had no complaints. Those would be a fun crop to have growing in the garden!