Weapon mods - how many tiers are there, and where can I purchase them?

I just got my first epic/purple machine gun. It has all 4 slots available to upgrade.

My question: what are the best mods to throw in there?
I have tier 1, 2 and I think even tier 3 mods. Obviously the higher the tier, the better the mod?
More importantly though, where can I purchase higher lvl mods? All I know about is the farm place, but there are only white, tier 1 mods available there iirc.

Generally speaking, can someone recommend a site or a wiki where all the differences and upgrades are pointed out and listed?

Thanks in advance!

Regarding this topic: can someone also link a site (if it exists somewhere) where all the sight mods (scopes) are not only listed, but also shown? In terms of how it looks like when you go into aim mode.
As it turns out, it is a pain in the **** sometimes to grab the wrong scope upgrade. In my case, I modded my LMG, only to find out that the flashy sparkly bullet storm hurts my eyes like a ***** and also I lost complete sight of enemies. The whole screen literally lit up like a firework. So I decided to detach it again. This slot on an LMG, at least for me, is rendered useless.
It really becomes unplayable after just emptying one magazine lol.

An option would be cool to reduce the light effects in game.

Check "mods" vendors and so far highest Ive seen was III.

Ive done some experiment... it seems you need to have same synergy for your weapon and mods, lets say your weapon has "veteran" synergy, you need to find "veteran" mods for it.

Quote:

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Originally Posted by Fiancee

Check "mods" vendors and so far highest Ive seen was III.

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I only know of the one at the Iron Demon Ranch. Maybe I should take a look at the 'Vendor' icons on my map next time I play. So far, when I've wanted a quick mod, I've just headed back to the Ranch if a mission hasn't given me something I can use =\

Quote:

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Originally Posted by SlashZaku

I only know of the one at the Iron Demon Ranch. Maybe I should take a look at the 'Vendor' icons on my map next time I play. So far, when I've wanted a quick mod, I've just headed back to the Ranch if a mission hasn't given me something I can use =\

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I dont know if a mod vendor follows suit, but there are several vendors that only appear once you clear the little mini-event nearby, such as the vendor that sells the orange HEMI Challenger.

I've only seen up to 3(blue), but since the game color codes all the way up to orange, I suspect that there are 5 in total.