I have only found the data for anhydrous form. I have no acces to JCPDS databae. Can you find the compounds by chemistry? Then it is way to go for you.
you can post your xrd RAW data so I can help you to identify the phase you are looking for using HSP software. I found this card. Potassium Tris(oxalato)ferrate(III) Trihydrate (K3 (Fe (C2 O4)3) (H2 O)3).