I managed to find a reference to R Wallace and Co, and as far as I can make out, they appear to be long gone, but I will do a little more digging to see if I can find out a bit more. Below is the entry in Grace's Guide to British Industrial History:
'R. Wallace and Co of Kilnfield Gardens Colchester
Specialists in Bulb Culture, Landscape Gardeners, &c.
Established in 1878 by Dr. Alexander Wallace.
1914 Present Principal: Robert Whistler Wallace, J.P., F.R.H.S. Premises: Cover twenty acres. Fully stocked. Staff: Forty. Specialities: Choice Bulbs, Lilies (chiefly), New and Rare Hardy Plants and Bulbs, Landscape Rock and Water Gardening.'
So this gorgeous Iris has been available to the public for a hundred and twelve years! My mind wanders as to which gardens it might have graced in that time. This is what I call the 'Romance of Gardening' - all those varied people, with different stories to tell, all fixing on the same plant as me, in different places and different times. More research needed!
As this particular specimen is now getting quite large, I will will probably have some divisions available for sale in August (UK only). Drop me a message if you are interested, in the comment box below!
Happy gardening!