Orbignyi and reticulatus, possibly magdalenae, may work, though I'd still recommend larger tanks for them. All three are occasionally available; I saw some smaller imports of reticulatus and orbignyi (mislabeled as "columbian hystrix") earlier this year. Supposedly there's a breeder working with orbignyi over in Germany; I don't know of anybody in the US. Reticulatus are some of my favourites; definitely less interactive and much shyer than motoro, though.