Call me stupid but how do I unlock the new weapon mods?

Only with mfunds from item store 

Don't... don't ever buy the UR weapon/character... don't ask... just don't do it...

Unless you have already unlocked everything (not completed full manifest, just unlocked everything), I would save those Missions Funds for UR unlocks and Equipment. Rares, you can get plenty from Premium packs or from Expert packs. But a 100% drop you can't get bar from that occasional Apex Pack. So best to save for those.

For the mods, you can do just as well with the normal ones until you gain better weapons and character kit unlocks. Once you reach a certain stage, you will know when you go for the weapon mods.

As mentioned, only with Mission Funds. But...

I don't consider virtually any of the new "compromised" (get one thing, lose another) to be worth it. The exception are the AR and pistol targeting (without scope) mods.
Sure, some of the others will be superior on a few builds. But not on most compared to the "vanilla" I already have. And it is always RNG.

If I knew they were going to do this, I would have bought a lot more UC and Rare original weapon mods with my MF. Now, I'm just accruing them. I have way more than enough for the remaining equipment (unless they add more). So what to buy? Either uber-expensive UR's or rare weapons. Sure, I can get the latter with Expert/Premium packs. But for us non-Platinum players, why not get them quicker?

If you buy item mods from the item store, it might give you normal weapon mods of that rarity if they are not maxed.

The silliest part about the loot progression other than its absurd pool size is the way it is unlocked: Characters first, Weapons second, Weapon Mods last.
Thus you won't be unlocking Weapon Mods of a given rarity tier regularly until your Characters as well as Weapons of that rarity tier are fully maxed.
It is goes without saying that this is a very a silly system that makes the game unwelcoming to any player other than the hardcore ones.

Nope.  They only give the non-standard ones.   

That is false, or at least used to be. They definitely never preferred standard ones, they were just included in the pool. I guess I can try it again whenever uncommon mods come back.

LMAO!!!