Head Financier of Mechagon

[npc=154960] can be efficiently farmed with almost no downtime; just try to pick up some hour outside the peak hours which helps achieving this (flying is naturally quite mandatory for this). Each armory costs 200 [item=166846] and a [item=166970] to build and yields 11 contributions for the achievement. Thus one full round described below nets you 77 contributions in the best case scenario. If you are planning to do the achievement mostly with armories, 1000 contributions equals roughly 91 armories build which is 91 [item=166970]s and 18 200 [item=166846] (~73 [item=169610]s). In practise, the required materials needed is most likely a bit more since one can assume you are dropping contributions to other (more expensive) contructions as well while doing Mechagon.

There are 21 armories spread around the Mechagon and they are divided into seven clusters each having three possible spawn locations. Only one armory per cluster can be up at any given time. This coupled with the fact that each armory lasts for 10 minutes followed by a short respawn time of 4-5 minutes makes the grind much more predictable.

With this information you can estimate the cluster which will spawn the armory next and go circle the three possible spawn locations for that cluster. Even if someone else manages to complete the armory before you, you can look how much time there's left on the [spell=290888] from the [npc=153288] hanging around the armory and calculate a rough estimate when the armory was built. This way you can be ready to camp in that cluster on the next round.

I basically flew between the seven clusters while keeping a note at what time each of them had their armory built the last time. After ~14 minutes I came back to that cluster to wait for the next one to pop. I managed to do about 500 contributions in 1,5 hours and I missed only a handful of spawns to other people with this tactic.

Here are the coordinates for each spawn location for every cluster:
/way 15.46, 81.24 Western Spray #1: West Island
/way 21.66, 80.89 Western Spray #2: East Island (south)
/way 23.62, 74.70 Western Spray #3: East Island (north)

/way 37.09, 48.02 The Fleeting Forest #1: Next to Danielle Anglers
/way 39.30, 39.08 The Fleeting Forest #2: On the beach
/way 45.42, 49.93 The Fleeting Forest #3: On the the mountains

/way 49.78, 35.69 Scrapbone Den #1: Near the lake in Fleeting Forest
/way 55.03, 25.43 Scrapbone Den #2: On the hills to north-west
/way 59.68, 23.73 Scrapbone Den #3: In the middle of the Den

/way 57.60, 52.28 Crashcog Circuit #1: On the north-east tower of Junkwatt Depot
/way 58.84, 48.09 Crashcog Circuit #2: On the platform below the location #1
/way 61.84, 36.62 Crashcog Circuit #3: Next to the Charging Station

/way 66.36, 35.30 Rustbolt #1: Just outside of the western entrance of Rustbolt
/way 73.61, 24.38 Rustbolt #2: Next to Horde flight master
/way 77.55, 40.02 Rustbolt #3: Next to Alliance flight master

/way 68.98, 49.36 The Heaps #1: On the west side of the hill
/way 71.92, 50.65 The Heaps #2: On top of the hill, next to Scrap Kings spawn location
/way 79.95, 48.31 The Heaps #3: On the beach to the east, south-east from Alliance base

/way 71.28, 66.93 The Outflow #1: On the hills behind the Reclamation Rig
/way 79.20, 56.51 The Outflow #2: North-east of the area, on a gear
/way 81.64, 62.88 The Outflow #3: East side of the area, next to the ocean


Sidenote:
The Flame Turret spawning also works the same way and their locations are also in clusters of three. However, they aren't really good for this achievement as you can only get one contribution per turret, but they are nice when doing the Junkyard Machinist.

Armories are the best way to progress this achievement: they take 200 scrap, 20 at a time, and 1 energy cell. In addition to that, you're pretty likely to find them when they're not built: They last ten minutes, then once they fade another armory immediately becomes available to build on the island.

Drilling Rigs are not a bad way to progress either, at 25 scrap a pop. However, they spawn slower and are more likely to see others contributing.

Edited with new information, thanks in part to Lyli01. :)

Awesome comment. Exactly the info I was looking for. Only thing I'd add is that the full cost of the armory is 200 Spare Parts + 1 Energy Core (11 contributions) meaning that the full 1000 contributions is around 18200 Spare Parts + 90 Energy Cores