Are you collecting them in strikes. Has to be done in a strike. I recommend loading up the night fall. Change into your best gear, but leave on the solstice gloves. Run an arc subclass with all arc weapons. Kill all the enemies at the start except for 1 Minator, collect orbs. Rinse and repeat. Took me about 30 mins. Since most of the enemies are yellow bar you get heavy ammo and 2-3 orbs per enemy. You need to collect around 100 orbs.