You can easily find yuca in most regular grocery stores, in Asian or Latin American specialty markets and of course, Amazon. This post from Food52 gives you some info on what to look for when buying yuca, as well as how to store it.
1. Before you begin: If you are using a fryer, you can make sure it is all set up now, and heating up. If you are frying in a pan, just add the oil to the pan and leave it over low heat, just so it warms up, but not too hot to get to temperature too fast – I highly recommend you use a thermometer to help you maintain the temp at 350F