There are a number of maps that cover the whole of NSW. The two that leap out are Blitzortung.org – which appeals because of its open source nature; and weatherzone – which you can find reproduced all over the place. The fact both these services cover a huge area, though, means that during a storm Sydney just becomes an indistinguishable mess of lightning strike icons.
Update: There’s also lightningmap.org which has real-time monitoring and prettier presentation although it appears to be based on Blitzortung information.
Everything else you’ll find on a search is just the Weatherzone map which has been reproduced everywhere.