I’ve been looking into Crataegus arnoldiana, and it appears that some authorities treat it as a large-fruited form of Crataegus submollis. I’m not sure whether this interpretation applies to all large-fruited forms of C. submollis or only to descendants of the trees originally found growing naturally at the Arnold Arboretum.
@JohannsGarden recently posted that he tentatively identified the hawthorn cultivar ‘Angelo Rosso’ as Crataegus submollis. ‘Angelo Rosso’ may be a good option for anyone looking to acquire a tree similar to the one shown in @trav’s photos.