It's not on the UK list of about 50,000 dahlias nor on the Big List. It's quite likely that the company took some other dahlia & renamed it & sold it under a new name--NOTE that company is noted for selling endangered plants.

Winchester Growers Ltd. had it listed on a "wanted" list. Now it is marked "found THANKYOU." They say that they are holders of the National Dahlia Collection.

The Royal Horticultural Society Plant Finder indicates one other UK supplier for 'War of the Roses' at the location indicated below. However, there still seems to be no North American supplier offering this variety.

Here is a link that might be useful: RHS Plant Finder

I still haven't found a source in the US for this dahlia variety. Here's a link to a photo and description:

Here is a link that might be useful: Dahlia 'War of the Roses'