As u all know Margonites are all over the place in NF
The trick of the day is finding a high enough concentration of margonites that isn't a pain in the ass (i.e, u don't have to become a fucking worm)
A few NF missions provided this:
The Grand Court of Sebelkeh is one, but u will need a party of almost full size to do it as a farm because u have to keep the Lyssa alter from becoming a margo shrine and thus failing the mission and ending it.
A better choice is Nundu Bay.
Because its also ALL margonites AND u just have to keep Elder Jonah from dying. just sit there (with Melonni, which we will discuss her in a minute) and kill the margos as they come in the area. You can do this as an SoS solo actually...with Melonni ofc as required for the mission.
Heres the SoS solo build I used (no, there is no heal to it, u have Melonni), as an Elementalist with an 11 communing, 11 channeling and a 10 (8+1+1) energy storage:
>Disenchantment (Margo reapers are dervish and u WILL need this spirit do disenchant them.)
>Signet of Spirits (Elite)
>Armor of Unfeeling (ALWAYS use this with ANY SoS Solo build when you are farming foes above the level of the spirits you are using in general to avoid critical hits against them.)
>Summon Spirits (This is more so to heal ur spirits here than anything else.)
***before the real fun starts u will need to get the Vial of Purified Water skill from Elder Jonah. When u do this is the easiest skill to do without to get the his skill
And here is Melonni's build (Note: this is actually the dervish RA healer build, except that a rez skill (Resurrection Chant) has been added where Shield of Force would normally be):
>Signet of Pious Light
>Life Sheath (Elite)
>Resurrection Chant (This is just insurance, u likely wont need her to use it. Well, not for the first part anyway.)
Earth Prayers:8, Mysticism:10 Protection Prayers:12 Healing Prayers:2 (this just uses the left over attribute points for Resurrection Chant). Use whatever staff or wand/focus set u have handy. No need for anything special.
How it all works.....
Don't get the skill, Vial of Purified Water, from Elder Jonah right away, it triggers the real mission start. Instead use a long/flat bow and pull the margonites into u, one group at a time. The NPC's here will help u kill them off. Do this with all 7 groups on the immediate outside of the territory. Flag Melonni around as u need her. This whole thing takes just around 10 minutes.
You could just resign (and then repeat) here if u want, u likely will have 4-6 margo masks by this time. But if u want to continue on NOW talk to Elder Jonah and get the skill.
At 1st the margo waves come in at groups of 2 then groups of 3, then 4, the Harbingers come in alone. The Harbingers can drop Demonic Relics, save them, Nick will ask for them later.
Your life at this point will likely be short, either u and Melly-Mel will get overwhelmed or Jonah's healing skills will seem to never target himself and he will die. Just hold out as long as u can, u will end up with a few more masks through this.
if by some stroke of serious luck or skill,
u survived all of that jolly cluster-fuck, there are margo groups scattered all about the landscape that u can pick off at your whim.
That's what I got.