M, do you have what we call on this side of the pond "big box stores" ? An equivalent to Home Depot or Lowes? They carry anything from cleaning supplies to lumber to appliances to carpet. The flex duct will be in the heating/ furnace filters etc. area. If they don't have the same dia. pipe there should be reducing adapters to make a conversion. If not there, try appliance repair or an HVAC/furnace seller.