You can get 0.1% tolerance resistors quite easily and cheaply, especially if you are prepared to use SMD components. See http://uk.farnell.com/jsp/search/browse.jsp?N=203968+110075262+110079727&Ns=P_PRICE_FARNELL_UK|0&locale=en_UK&appliedparametrics=true&getResults=true&suppressRedirect=true&isRedirect=&originalQueryURL=/jsp/search/browse.jsp%3FN%3D203968%26No%3D0%26getResults%3Dtrue%26appliedparametrics%3Dtrue%26locale%3Den_UK%26divisionLocale%3Den_UK%26catalogId%3D%26skipManufacturer%3Dfalse%26skipParametricAttributeId%3D%26prevNValues%3D203968 for example.