i've seen it almost everywhere - autobahn, repco.
good stuff the 300 gear oil.
Get some redline if the Motul is harder to get. Either buy it RRP or this guy, Harold:
http://www.performancelub.com/index.htm
The best prices on redline you will get by far.
However also look into castol gear oils, decent quality for a cheaper price.
I use Redline in diff, box and engine. Seems to go good and has longer OCIs.