Wow, this identical query comes up. A lot. El Mercado, La Unica, Deliberico, F&O, Sam's -- all for chorizo, Mercado and La Unica for morcillas as well. Buenos Aires Deli (?) is another option.
Often (always?) folks inadvertently confuse fresh, Mexican chorizo (found literally in every grocery store in Chicago) with dry Spanish chorizo (harder to find, but widely available). Look for the Palacios brand from Rioja (Spain), which is to my taste the best normally available in Chicago. Certainly available at Sam's and La Unica, probably F&O and Deliberico. PS, El Mercado's morcillas are quite good and likely close to what you had in Spain. Only problem is Mercado doesn't always have the Palacios chorizo. The always have other brands that are ok.