Propably I make FO by oxidizing Ferrous Oxalate with oxalic Acid and Perhydrol ( 30% H2O2) but i don't have magnetic stiller .. ( ok my english is not good.. )
Do an APUG search on your question and you'll find more information about making FO. There is at least 1 or 2 longs threads about this topic.
I think you will end up spending a whole lot more money learning how to make FO than if you purchase it. My advice is to buy it to make prints with and once you know how to do that then you might want to consider making your own. Ferric Oxalate is not a well defined compound and is difficult to make a highly pure form, though supposedly few palladium printers do.
To illustrate the difficulty read this thread:
(there was a url link here which no longer exists)
Post your question on the ALT Photography list and you will probably get more info about making your own.