I always liked Economic Intelligence Unit's reports on Nepal. I have bben following it over the last twenty tears. They are the best for consumer price index. Try a good library. Alternatives are the Website of World Bank, International Montetary Fund, Asian Development Bank. As a marketer I also heavily rely on International Marketing Statistics that comes out annually and is published by Euromonitor PLC in USA and London. They come in hard copies and you might have to pay online. Do they cover back fifteen years? Yes, they do. Try a good old USA University library. If it is available in Australia then in USA it could be very probable. Good luck hunting the info.