So I used the genuine transfer case oil at mental per litre, but with alternatives so hard to come by in Aus, I sucked it up. Same for brake fluid. The funky spec was too hard to sort here independently so paid for the genuine article. Gearbox I use a Motul ATF VI and engine Penrite C4. Diffs were Castrol spec aligned to factory, purchased commercially. Filters I use Mann.
I change the engine oil more regularly than specified. Gearbox oil I'm dropping 4L every year to freshen the 200k oil that's in there. If I drop 4L every year it will remain fresh'ish', is easy enough and not a high cost.

