You don't have to, you should be able to buy the flour, potatoes, eggs and seasonings from your usual grocery store. However, if you want to use 00 Italian flour, you might need to visit a specialist grocery store or ask your local bakery to sell you some. Such flour can also be purchased online in many countries. As for the potatoes, if you're not sure if they're Russets, Yukon Gold or any other suitable potato varieties (all-purpose or floury potatoes tend to be best), either ask the supermarket attendants or visit a specialized fruit and vegetable seller/farmers market stall.