Fabada is always made with white beans, called fabes in Asturian. The bean variety “faba de Asturias” is a white kidney bean. Here in Valencia we find similar beans called alubia blanca, while in the US a good substitution would be cannelloni beans.
From here…
https://juliaeats.com/2017/04/02/fabada-asturiana/#:~:text=Fabada%20is%20always%20made%20with,substi tution%20would%20be%20cannelloni%20beans.
I’ve made it with cannelloni beans myself. Couldn’t get morcilla so just used extra chorizo. Tasted just fine… authentic - no. Edible - o yes.