You can buy non-branded Canon NB-xL batteries at a much cheaper price on Amazon. When I bought my SD1000, I picked up an extra battery for $5.99 compared to $34.99 for the OEM Canon battery.
I don't think you'll get the manufacturer to sell you a battery or 2, look for non-branded cells.
I just bought a G10 and there is a non-OEM NB-7L on Amazon for $6.99. Look at the price difference here: