Did some reading on Wikipedia on the NV3550 (NV3500) which lists non-OEM fluids certified to meet MS-9224. Tried Pennzoil but no longer in Australia. Got onto Amsoil in Sydney who have quart sized containers (964ml) for $22 each. Quoted freight was $16. So that's pretty good in comparison to the dealer rip off.
Also called Penrite in Oz and they said the Pro-Gear 75-90 is suitable but don't have details on it being MS-9224 compliant. Also seems like that particular one isn't widely available.
After all that I found this old thread which goes through a similar discussion.
http://www.ausjeepoffroad.com/forum/...ion+oil+change
Hope that is of use to someone. Probably not many of the 2.5 manuals around anymore.