From a purely practical and economic perspective making Ferric Oxalate for pt/pd printing is not worth the trouble IMHO. Even the method described on jeffrey mathias website, which Jorge describes as far easier than the traditional method, takes many, many hours to complete, and in the end yields only about 125g of ferric oxalate powder.
And, compared to the costs of the platinum or palladium salts, feric oxalate represents a very small investment in the overall cost of pt/pd printing. A hundred grams of ferric oxalate from Artcraft costs $50, enough to make over 400ml of the working 25% ferric oxalate solution used in Pt/Pd printing. By contrast, an equal amount of 20% palladium or platinum solution (based on prices at B&S) will cost between $800-1400.