you usually buy sodium metabisulfite, check places that sell supplies to make wine or beer, sodium sulfite works similar, you can make ferrous sulfate, with Iron and sulfuric acid, there is information on forum for that, or it can be bought at garden centers.
with these chemicals pay attention to suffix --ate --ite --ide
there are many chemicals we use for processing these metals, and some mixtures can be very dangerous, search forum and you will see them and some sources, study the safety of these,
you will need to find the process you intend to use, and study it well before, you start dumping chemicals together, learn proper disposal methods also. most of this is a learning process, the little gold you get will be secondary, and if you dont learn you dont get gold.and can harm yourself and others, so start studying and reading so you can get them pretty metals.