my 2002 e46 325i trans was fully rebuilt, they refilled it with Penrite full synthetic (it as 8L for a full fill from dry) ATF F5. It's still running nicely - and shifting really smoothly - since Jan 2013, around 60k kms... oh, nearly time for a precautionary change!
You should be able to source it in 20L barrel or enviro-box... as you're doing two, may pay off in bulk-buy saving. http://penriteoil.com.au/products/atf-fs-full-syn
You might consider doing a drain and fill, running it for 500-1000kms, then doing the full drain, pan clean, filter replacement etc, and refill... there are pros and cons, and plenty of opinions. Other option (which I did for my Volvo: the home driveway 'power change' ... draining 1.9L each time via the outlet pipe from the trans into the cooler, shutting off, replenishing with fresh fluid, re-starting, running through the gears, then draining out another 1.9L, rinse and repeat until nice raspberry coloured fluid came out again (14L DEXIII in total). Worked well. HTH.
EDIT - I see REPCO advertising Oil Bonanza (50% off) this weekend. Let them buy your business! Read the fine print - it's probably *not* restricted to store stock.