Sorry if this has already been mentioned as I haven't read the whole thread. Silversmith/Goldsmith/Coppersmith/Ironsmith type buildings that give the Bullion resource require one of the metal map resources (with mine and route) in the city vicinity, a silver/gold/copper/iron mine building in the city, and a forge. These buildings should require either a forge OR a foundry, as foundry replaces forge (*edit to add, that if foundry can later be replaced by another building, that should also be an 'OR' requirement, IMO it should be any one of the buildings in that upgrade chain that is required, rather than just the first one, at least up to the point where jewellers and anything else requiring Bullion resource becomes obsolete!) - in my current game I have accidentally ended up not being able to get the Bullion resource (and cannot build jewellers as a result), by upgrading my forges to foundries without having first built the relevant metalsmith building, which is now unavailable to build unless I delete a foundry somewhere (assuming I can remember how to do that!) and rebuild a forge.