I don't know where you are looking, but as far as I am aware Great Eastern Models is the only mainly model railway shop in Norwich ( and not just 00 ). There is Pegasus Models which is mostly R/C, but is good for some materials. And there is Kerrison toys which has a small modelling section upstairs. These three are all on the city outer ring road so you will need a car to get to them. If you are stuck in the city centre there is a very good toy shop in the Royal Arcade called Langley's, which has a small but good model section, upstairs again. Then there are the Games workshop shops, there are supposed to be 3 but I have only visited the one opposite Jarrold's department store . And finally there is Thorns hardware shop which is always worth a browse . There is a shop called Jumblies which is just out of Norwich, which I believe specialises in diecast collector models.
One thing I would recommend is phoning any shop you intend to visit and making sure they will be open, or indeed still in business. There was a model shop in Wroxham that changed venue three times in as many years before disappearing in a puff of smoke .
Apart from that Norwich really is a lovely city, with lots of pedestrianized streets and narrow alleyways, to get lost in. A very good market in the centre with lots of food on sale . Hope you have a nice visit .