Yuca's all over the place. Most Mexican and Puerto Rican groceries have it, as do African stores up north. Westbrook Market in Westmont has it. But to be completely honest, fresh yuca is pretty hard to deal with, and it is often skunked. Powdery insides from poor handling is common. Good, clean, ready to cook frozen yuca, mostly grown in Costa Rica, is in many Latino grocery sections. The natural place to start looking for fresh or frozen is La Unica, the Cuban/South American superstore on Devon.
Do yourself a favor and cook the yuca in a pressure cooker, then fry it up in some lard with mojo criollo and onions.