Do 37 public events on Earth (gold rating & use public event tracker to find these). Those will give you enough vanguard marks to buy a legendary gun. If you do just one event a day then the gun is yours in 37 days. For a piece of armour you need 75 Vanguard marks so that will take just 19 public events, so 19 days. You also need to do enough patrols to get to vanguard level 2 to be able to buy the armour or level 3 to buy the guns. But if you see public events and patrols as too much of a grind then I guess you have already got the most you can get out of the game and it's time to move on. Forgot to add that you also get a package from the postmaster for the first daily public events - this gives you an extra 2 vanguard marks - so its even quicker than what I wrote above if you just do one event a day - you also get a coin or mote of light from the post master and occasional shards and energies just after the public event ends.