I was in Tucson in April, too late for the CSSA Convention, unfortunately, but I still went to a few of the local nurseries.
This was in full bloom at Tanque Verde nursery
and this M. guerreronis also
And at Bach's Cactus nursery these great plants:
and M. baumii
next was M. lenta
then a few smaller plants (!)
and finally a modest (!!) M. crucigera
Fantastic....let alone all the other plants at each and every place.