Have you considered using Oxtails? I only mention it because the Kroger near me usually carries them so perhaps they do elsewhere. I've made them before using a braising technique and served them over mashed turnips with a spiced honey/clove sauce. They were damn good. Could work well for your tacos too.
UDS'55&16, Akorn, Bar-B-Q Kettle, mini WSM, Drum Grill. I'm JD.