The leaf surface of an Haworthia may be smooth and shiny or it may rough and bumpy. H. koelmaniorum is certainly an example of the latter. In our experience it's slow growing and reticent to develop offsets. Therefore it's not that available through nurseries, including our own (though we do have a couple available currently).
As with fans of Lithops, those of us who enjoy Haworthias will often be seen with a magnifying glass admiring the intricacies of their form.