You could try Amazon:
http://www.amazon.co.uk/Battle-over-.../dp/B000CDH7CO expensive though! You may need these:
http://www.justflight.com/supportfaq/battle-over-europe (BOE update packs)
On UK ebay there is usually a copy for sale, again though not cheap, good luck though.
Just flight only have Operation Barbarosa for sale and that just a download. Ebay would probably be your best bet.