When Marcus Ryan was over in the UK I went with him to Pan-Global Plants run by Nick Macer. Nick is one of a growing band of plants people who travel to collect good plants from all over the world. One of his interests is Agave and he has been selecting good forms including this species, Agave montana which is new to the UK. It was collected at 3,000m in NE Mexico and he says that it is one of the most handsome of Agave species forming a stunning rosette eventually up to a meter across. It could also prove to tolerate cultivation outdoors in the UK but this is likely to require a perfect well drained site.
I suspect that initially availability of these clones will be quite limited but in time they should become much more available.