I haven't come across this name as a Trade name nor as a synonym Evan. It seems to be one of those names the trade had conjured up for a form of the species, there is a bigger form of speciosum.
On Aroid.org it has been listed as a 'legacy entry' which is not an officially named variety.
http://www.aroid.org/cultivars...
The RHS doesn't recognise it, there are three varieties listed of which only one is accepted and recognised.
http://apps.rhs.org.uk/rhsplan...
I think the common name is being used, it is mentioned as "Giant Himalayan Cobra Lily" here..
http://www.bjdimages.co.uk/pho...
This site says it's Arisaema speciosum var. magnificum although their spelling is way off! That is not found in literature, Arisaema speciosum var. mirabile is which I think would be the bigger one.
http://www.edensblooms.com/pro...
Arisaema speciosum 'Himalayan Giant' is an amazing form of Arisaema speciosum, which often goes by the invalid name of Arisaema speciosum var. magnificum. It is simply a giant race of Arisaema speciosum discovered in India
http://www.ideamarketers.com/?...
I'm only finding results from the US using this, if you want to add it I would put it as a common name "Giant Himalayan Cobra Lily"
