Don't understand your question. Most potatoes either Irish or sweet are vegetatively propagated. Several cultivars of Irish potato have been recently introduced as seeds. Best known is Zoluska. There are a multitude of vendors for Irish potatoes. They sell disease free tubers, which you cut into pieces and plant. Sweet potatoes are sold as slips( small sprouts which are pulled off the sweet potato root). You can of course just save some of your harvest (either type) and use them to start next years crop.

You can usually buy seed potatoes from a Co-opstore or farm supply place.

As others have said you can always buy seed potatoes - at proper planting times - at local feed supply, farm stores, Co-Ops, Walmart, Home Depot, even many local grocery stores. Or you can order them numberous places online.

I use Ronnigers - linked it below.

Dave

Here is a link that might be useful: Ronnigers Seed Potatoes