TBH there is not a good way to farm for those other than the weeklies. I forget the name of the area, but in Venus where you spawn in for the Nexus raid, there are Vex and Fallen enemies that never stop coming. Just stand in a spot and kill away for engrams. Same thing with the spawn in area on mars. Go to the bottom of that area and kill Vex and Cabal. Stay there long enough and a little war between the two will start with many more enemies coming. But without gold, you're chances are completely random.