There is no particular place to find an original dial, you would have to hunt everywhere. Look at eBay, follow auctions, network with collectors. In a few years of diligent searching you might find one. But keep in mind that it will not be easy for you to know which dial is the correct size for your watch, most original dials will be in very poor condition, and a dial that fits your watch might look very different from the current dial. I have been looking for an original dial to replace the refinished dial on my father's watch for more than 10 years, and I still haven't found one that I am happy with. Overall, I would not personally bother trying to find another dial. That is your grandfather's watch, the value is mainly sentimental, and it doesn't look bad as it is.
Because of the small size and condition, the watch doesn't have much collectible value, maybe 200 Euros, or something in that neighborhood.
