Given that you're asking on the UA subforum, the UA way to get *G is to:
1. Take 4 united flights
2. Spend (slightly less than) $200,000 on UA credit cards. Probably easiest to do this on the United Club Card.
If you can open an Australian credit card, there is a Star Alliance card in Australia which offers a path to *G through spend as well. There should be ways to get *G through Air Canada Aeroplan via credit card spend as well, but I am not familiar with those.