If you can't do any temperature control of the fermentation (steady at around 10C) you may be better off sticking with the Gervin and doing it as an ale fermentation. It won't be a 'proper' lager but will probably taste better than a poorly controlled fermentation with a lager yeast.
One of the online homebrew shops will send you a few sachets at cost, I know Hop & Grape and The Hop Shop will, can't speak for the others. I would offer but I don't have any.