How do you unlock specific weapon mods in Fallout 76?

I've jumped into Fallout 76 with a burning desire to craft myself a nice rapid firing pipe pistol with a big drum magazine.

From what I can tell very limited weapon mods are available at the beginning & you need to unlock mods to improve your weapons. You also need perk cards to enable the more advanced unlocked mods.

So far I've been rewarded plans/recipes/mods for completing quests. I also think I've found a mod or two during general exploration looting.

My question: Is there a direct way to unlock mods for specific weapons?

For example does scrapping the same weapon type give access to mods? Can we purchase mods? Or swap mods with other players?

Any help appreciated.

From gameplay last night:

1. Scrapping weapons gives a chance of unlocking a mod for that specific weapon.
2. You can buy single use mods from vendors (but the range isn't great).
3. You can but plans from vendors that enable you to learn how to craft a mod (but the range isn't great).
4. You can only share mods when they are items in your inventory.

So in short the best way to get mods for a specific weapon is to gather lots of that weapon & scrap them.

As an example our team fought through dozens of Super Mutants around Summersville & New Gad. Many Super Mutants carried hunting rifles & at a rough count every third rifle I scrapped unlocked a mod. By the end I had upgraded my hunting rifle to a basic sniper rifle or sorts.