Mersyndol is essentially the same as Pandeine (Paracetemol + Codeine) but with the addition of a small amount of doxylamine succinate (an antihistamine).
Normal Mersyndol is OTC, but you'll more than likely have to ask for it (like nurofen plus). Mersyndol Forte is prescription only.
Rikodeine is OTC. Again, it's a pharmacist only medication which you'll have to ask for, but no script needed.
My Dr is a pretty useful site, particularly the consumer medicines information index which has all the info you would normally find on the little consumer medicine info flyer that comes with your pharmaceutical items.
Failing that, like Marly suggested, google in your friend. If you search for whatever medication and OTC/prescription, you should be able to find out pretty easily what schedule something is by looking at online Australian pharmacy sites.