You might have difficulty sourcing Gerard Dubois champagnes. They're primarily sold to trade outlets (e.g. wine bars and hotels) and aren't seen that often in retail outlets.
Your best chance of finding some might be to ask the producers who they supply in the UK. Send an e-mail to
[email protected]
You'll also need to take care that you get the right style of champagne. To see the Gerard Dubois range (and to see if the label looks familiar), click 'Nos Cuv�es' here:
http://www.champagne-gerard-dubois.com/
Chris